[chore] Update Azure Event Hub Receiver Documentation (#28623)

**Description:** <Describe what has changed.>
<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
The Documentation surrounding Azure Event Hub Metric creation is
out-of-date or not accurate.

**Link to tracking Issue:** <Issue number if applicable>

#28622

**Testing:** <Describe what testing was performed and which tests were
added.>
No code was modified, only documentation.

**Documentation:** <Describe the documentation added.>
Updated the README.md in reciever/azureeventhub to be more accurate and
improved the Metric mapping table to be consistent with the Log section.

Author: cparkins

.chloggen/eventhubreceiver-update-readme-for-metrics.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: azureeventhubreceiver
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Updated documentation around Azure Metric to OTel mapping.
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [28622]
+
+# (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: []

receiver/azureeventhubreceiver/README.md

@@ -100,20 +100,21 @@ JSON numbers are encoded as doubles.
 For Metrics the Azure Metric Records are an array
 of "records" with the following fields.
 
-| Azure      |
-|------------|
-| time       |
-| resourceId |
-| metricName |
-| timeGrain  |
-| total      |
-| count      |
-| minimum    |
-| maximum    |
-| average    |
-
-From this data a Metric of type Summary is created
-with a single Data Point that represents the value
-from the "total" field.
+| Azure      | Open Telemetry                              |
+|------------|---------------------------------------------|
+| time       | time_unix_nano (field)                      |
+| resourceId | azure.resource.id (resource attribute)      |
+| metricName |                                             |
+| timeGrain  | start_time_unix_nano (field)                |
+| total      | mapped to datapoint metricName + "_TOTAL"   |
+| count      | mapped to datapoint metricName + "_COUNT"   |
+| minimum    | mapped to datapoint metricName + "_MINIMUM" |
+| maximum    | mapped to datapoint metricName + "_MAXIMUM" |
+| average    | mapped to datapoint metricName + "_AVERAGE" |
+
+From this data a Metric of type Gauge is created
+with a Data Points that represents the values
+for the Metric including: Total, Minimum, Maximum,
+Average and Count.
 
 [storage extension]: https://github.com/open-telemetry/opentelemetry-collector-contrib/tree/main/extension/storage