[pkg/ottl] Add event_name path to the OTTL Log context (#40311)

<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
#### Description

This PR exposes the `event_name` path in Log OTTL context.
Proto:
https://github.com/open-telemetry/opentelemetry-proto/blob/main/opentelemetry/proto/logs/v1/logs.proto#L224.

<!-- Issue number (e.g. #1234) or full URL to issue, if applicable. -->
#### Link to tracking issue
Fixes #40230

<!--Describe what testing was performed and which tests were added.-->
#### Testing
Unit test

<!--Describe the documentation added.-->
#### Documentation
README

<!--Please delete paragraphs that you did not use before submitting.-->

Author: edmocosta

.chloggen/ottl-add-event-name-field.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: pkg/ottl
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Add `event_name` path to the OTTL Log context
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [40230]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

pkg/ottl/contexts/internal/ctxlog/log.go

@@ -75,6 +75,8 @@ func PathGetSetter[K Context](path ottl.Path[K]) (ottl.GetSetter[K], error) {
 			return nil, ctxerror.New(nextPath.Name(), path.String(), Name, DocRef)
 		}
 		return accessSpanID[K](), nil
+	case "event_name":
+		return accessEventName[K](), nil
 	default:
 		return nil, ctxerror.New(path.Name(), path.String(), Name, DocRef)
 	}
@@ -331,3 +333,17 @@ func accessStringSpanID[K Context]() ottl.StandardGetSetter[K] {
 		},
 	}
 }
+
+func accessEventName[K Context]() ottl.StandardGetSetter[K] {
+	return ottl.StandardGetSetter[K]{
+		Getter: func(_ context.Context, tCtx K) (any, error) {
+			return tCtx.GetLogRecord().EventName(), nil
+		},
+		Setter: func(_ context.Context, tCtx K, val any) error {
+			if v, ok := val.(string); ok {
+				tCtx.GetLogRecord().SetEventName(v)
+			}
+			return nil
+		},
+	}
+}

pkg/ottl/contexts/internal/ctxlog/log_test.go

@@ -342,6 +342,17 @@ func TestPathGetSetter(t *testing.T) {
 				log.SetSpanID(spanID2)
 			},
 		},
+		{
+			name: "event_name",
+			path: &pathtest.Path[*testContext]{
+				N: "event_name",
+			},
+			orig:   "",
+			newVal: "exception",
+			modified: func(log plog.LogRecord) {
+				log.SetEventName("exception")
+			},
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {

pkg/ottl/contexts/ottllog/README.md

@@ -28,6 +28,7 @@ The following paths are supported.
 | instrumentation_scope.attributes\[""\]         | the value of the instrumentation scope attribute of the data point being processed. Supports multiple indexes to access nested fields.             | string, bool, int64, float64, pcommon.Map, pcommon.Slice, []byte or nil |
 | log.attributes                                 | attributes of the log being processed                                                                                                              | pcommon.Map                                                             |
 | log.attributes\[""\]                           | the value of the attribute of the log being processed. Supports multiple indexes to access nested fields.                                          | string, bool, int64, float64, pcommon.Map, pcommon.Slice, []byte or nil |
+| log.event_name                                 | the event name associated with the log being processed.                                                                                            | string                                                                  |
 | log.trace_id                                   | a byte slice representation of the trace id                                                                                                        | pcommon.TraceID                                                         |
 | log.trace_id.string                            | a string representation of the trace id                                                                                                            | string                                                                  |
 | log.span_id                                    | a byte slice representation of the span id                                                                                                         | pcommon.SpanID                                                          |

pkg/ottl/contexts/ottllog/log.go

@@ -59,6 +59,7 @@ func (l logRecord) MarshalLogObject(encoder zapcore.ObjectEncoder) error {
 	encoder.AddString("span_id", hex.EncodeToString(spanID[:]))
 	encoder.AddUint64("time_unix_nano", uint64(lr.Timestamp()))
 	encoder.AddString("trace_id", hex.EncodeToString(traceID[:]))
+	encoder.AddString("event_name", lr.EventName())
 	return err
 }