Allow indexing string slice type (open-telemetry#35581)

**Description:** Allow indexing string slice type. I can also add
support for other types such as []int if needed. Let me know if this
approach is good enough.

I haven't found a more generic solution, thank you for any feedback.

**Link to tracking Issue:** Fixes  open-telemetry#29441

**Testing:** Unit test

**Documentation:**

Author: lkwronski

.chloggen/lkwronski.issue-29441-slice.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: bug_fix
+
+# 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: Allow indexing string slice type
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [29441]
+
+# (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: [user]

pkg/ottl/e2e/e2e_test.go

@@ -1010,6 +1010,13 @@ func Test_e2e_ottl_features(t *testing.T) {
 				tCtx.GetLogRecord().Attributes().PutBool("isMap", true)
 			},
 		},
+		{
+			name:      "extract value from Split function result slice of type []string",
+			statement: `set(attributes["my.environment.2"], Split(resource.attributes["host.name"],"h")[1])`,
+			want: func(tCtx ottllog.TransformContext) {
+				tCtx.GetLogRecord().Attributes().PutStr("my.environment.2", "ost")
+			},
+		},
 	}
 
 	for _, tt := range tests {

pkg/ottl/expression.go

@@ -111,10 +111,15 @@ func (g exprGetter[K]) Get(ctx context.Context, tCtx K) (any, error) {
 				}
 				result = ottlcommon.GetValue(r.At(int(*k.Int)))
 			case []any:
-				if int(*k.Int) >= len(r) || int(*k.Int) < 0 {
-					return nil, fmt.Errorf("index %v out of bounds", *k.Int)
+				result, err = getElementByIndex(r, k.Int)
+				if err != nil {
+					return nil, err
+				}
+			case []string:
+				result, err = getElementByIndex(r, k.Int)
+				if err != nil {
+					return nil, err
 				}
-				result = r[*k.Int]
 			default:
 				return nil, fmt.Errorf("type, %T, does not support int indexing", result)
 			}
@@ -125,6 +130,13 @@ func (g exprGetter[K]) Get(ctx context.Context, tCtx K) (any, error) {
 	return result, nil
 }
 
+func getElementByIndex[T any](r []T, idx *int64) (any, error) {
+	if int(*idx) >= len(r) || int(*idx) < 0 {
+		return nil, fmt.Errorf("index %v out of bounds", *idx)
+	}
+	return r[*idx], nil
+}
+
 type listGetter[K any] struct {
 	slice []Getter[K]
 }

pkg/ottl/expression_test.go

@@ -59,6 +59,16 @@ func basicSlice() (ExprFunc[any], error) {
 	}, nil
 }
 
+func basicSliceString() (ExprFunc[any], error) {
+	return func(_ context.Context, _ any) (any, error) {
+		return []any{
+			[]string{
+				"pass",
+			},
+		}, nil
+	}, nil
+}
+
 func Test_newGetter(t *testing.T) {
 	tests := []struct {
 		name string
@@ -237,6 +247,25 @@ func Test_newGetter(t *testing.T) {
 			},
 			want: "pass",
 		},
+		{
+			name: "function call nested SliceString",
+			val: value{
+				Literal: &mathExprLiteral{
+					Converter: &converter{
+						Function: "SliceString",
+						Keys: []key{
+							{
+								Int: ottltest.Intp(0),
+							},
+							{
+								Int: ottltest.Intp(0),
+							},
+						},
+					},
+				},
+			},
+			want: "pass",
+		},
 		{
 			name: "enum",
 			val: value{
@@ -532,6 +561,7 @@ func Test_newGetter(t *testing.T) {
 		createFactory("Map", &struct{}{}, basicMap),
 		createFactory("PSlice", &struct{}{}, pslice),
 		createFactory("Slice", &struct{}{}, basicSlice),
+		createFactory("SliceString", &struct{}{}, basicSliceString),
 	)
 
 	p, _ := NewParser[any](