[mdatagen] Add functions for processing structured events (open-telemetry#12961)

<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
#### Description
Add functions for processing structured events

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#### Link to tracking issue
Part of open-telemetry#12571 

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

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#### Documentation
Added

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Author: sincejune

.chloggen/metadata-events-func.yaml

@@ -0,0 +1,25 @@
+# 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. otlpreceiver)
+component: cmd/mdatagen
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Add functions for processing structured events in mdatagen
+
+# One or more tracking issues or pull requests related to the change
+issues: [12571]
+
+# (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:
+
+# 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: [api]

cmd/mdatagen/internal/loader_test.go

@@ -250,13 +250,30 @@ func TestLoadMetadata(t *testing.T) {
 				},
 				Events: map[EventName]Event{
 					"default.event": {
-						Enabled:               true,
-						Description:           "Example event enabled by default.",
-						ExtendedDocumentation: "The event will be renamed soon.",
+						Enabled:     true,
+						Description: "Example event enabled by default.",
 						Warnings: Warnings{
 							IfEnabledNotSet: "This event will be disabled by default soon.",
 						},
-						Attributes: []AttributeName{"string_attr", "boolean_attr"},
+						Attributes: []AttributeName{"string_attr", "overridden_int_attr", "enum_attr", "slice_attr", "map_attr"},
+					},
+					"default.event.to_be_renamed": {
+						Enabled:               false,
+						Description:           "[DEPRECATED] Example event disabled by default.",
+						ExtendedDocumentation: "The event will be renamed soon.",
+						Warnings: Warnings{
+							IfConfigured: "This event is deprecated and will be renamed soon.",
+						},
+						Attributes: []AttributeName{"string_attr", "boolean_attr", "boolean_attr2"},
+					},
+					"default.event.to_be_removed": {
+						Enabled:               true,
+						Description:           "[DEPRECATED] Example to-be-removed event enabled by default.",
+						ExtendedDocumentation: "The event will be will be removed soon.",
+						Warnings: Warnings{
+							IfEnabled: "This event is deprecated and will be removed soon.",
+						},
+						Attributes: []AttributeName{"string_attr", "overridden_int_attr", "enum_attr", "slice_attr", "map_attr"},
 					},
 				},
 				Telemetry: Telemetry{