Publish to gh pages

[sunker]

This PR introduces two GitHub Actions to streamline the process of managing Playwright test reports. Publishing the reports to GH Pages instead of GCS (like this existing publish-report Action does) has several advantages. Using GH pages brings this capability also to the community. It also allows GH enterprise customers to configure access control for GH pages, allowing them to use secrets within their e2e tests.

Github already offers a set of Actions that can be used to publish pages. But they're not suitable for this scenario for the following reasons:

• They're not adapted for multi-sites. Running e2e tests using a matrix generates one report per job, which needs to be deployed under a path unique for its test scenario (grafana image, grafana version etc)
• They don't offer a mechanism for cleaning up and deleting old reports. This is problematic, as GH free only allows 1GB of data. The deploy-report-pages deletes any published reports older than the specified retention period.

I know putting these two actions in a parent directory breaks the convention in this repo, but they are so tightly coupled so I thought it still makes sense. Happy to hear your thoughts on this.

See example of the actions being used in a standard datasource plugin here.
Example usage in the plugin-examples repo here

[tolzhabayev]

not quite clear why it would be necessary, isn't it an example for matrix test with multiple grafana versions? (from mobile so maybe did not look it up properly)

[sunker]

No for this example, the matrix resolves multiple plugins. Could for example be in a monorepo where you repeat per plugin. Not sure how common it would be, but basically just want to highlight that it can be used in many different ways.