<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
#### Description
Adds a `pcommon.Map` to the Event struct to represent additional
metadata from the producer. These attributes can be interpreted by
consumers, such as `Watcher` implementations like the healthcheckv2
extension.
Since the long-term goal is to replace Event with a pdata.Log
(OpenTelemetry Event), introducing attributes serves as an intermediary
step. This allows for experimentation with subcomponents and more
fine-grained events without immediately committing to a full migration.
It extends the `NewEvent` constructor in a backward compatible approach
with a new optional `...EventBuilderOption` parameter. The
EventBuilderOption is a sealed interface which is implemented with new
methods like `WithAttributes`.
<!-- Issue number if applicable -->
#### Link to tracking issue
Fixes #
https://github.com/open-telemetry/opentelemetry-collector/issues/13210
<!--Describe what testing was performed and which tests were added.-->
#### Testing
Constructor unit tests, calls to generate Events from the internal graph
have not been modified.
<!--Describe the documentation added.-->
#### Documentation
<!--Please delete paragraphs that you did not use before submitting.-->
b288271b77