feat(otelcol.receiver): GitHub

[matt-gp]

PR Description

This PR adds the opentelemetry github receiver https://github.com/open-telemetry/opentelemetry-collector-contrib/tree/main/receiver/githubreceiver

Which issue(s) this PR fixes

Fixes #1702

Notes to the Reviewer

PR Checklist

• CHANGELOG.md updated
• Documentation added
• Tests updated
• Config converters updated

[clayton-cornell]

I'll do a second pass over the docs after the current round of suggestions are implemented.

If possible, we should try to document the blocks in the same order they are presented in the Blocks table. This isn't a blocker.. just a nice-to-have for consistency. If there isn't time or you decide it's not worth the extra shuffling, we can skip it for this PR and do it at some future time.

[clayton-cornell]

Would it be a good idea to expand the descriptions a little? For example, here we could put something like this.... (needs to be validated that my suggestion is accurate)

When enabled, this block allows the receiver to convert GitHub Actions workflow and job events into traces.

{{< admonition type="note" >}}
Ensure your webhook endpoint is secured with a secret and protected by appropriate network security measures.
{{< /admonition >}}

[clayton-cornell]

Is it worth mentioning here that there are some additional requirements? For example something along these lines:

Ensure you have the following:

- A GitHub Personal Access Token or GitHub App with appropriate permissions
- For metrics: Read access to target repositories and organizations  
- For webhooks: A publicly accessible endpoint to receive GitHub webhook events
- Network connectivity to GitHub API endpoints, for example, `api.github.com` or your GitHub Enterprise instance

[clayton-cornell]

Maybe we could expand the description slightly? Something like this? (or similar)

This component can collect metrics about repositories, pull requests, branches, and contributors.
It can also receive GitHub Actions workflow events through webhooks to create traces.

[clayton-cornell]

The upstream configuration for the GitHub receiver has ServiceName and IncludeSpanEvents fields in the WebHook struct. Do we need to note that these are not included in this component?