[WIP] Load test-build-info files into BootstrapForTesting

[jdconrad]

This loads the appropriate information required for entitlements in unit tests and then creates a function that can take in a Class<?> and return a PolicyScope.

This is still a WIP and needs the following:

1. Load the server policy
2. Look at the plugin descriptor file to see if we are modular or should use unnamed
3. Instantiate the entitlement agent with the appropriate arguments
4. Annotation or setting to disable entitlements in unit tests

[ldematte]

Parsing is already done in ttps://github.com/elastic/elasticsearch/blob/main/test/framework/src/main/java/org/elasticsearch/bootstrap/TestBuildInfoParser.java. See #127719

I would suggest to keep parsing separate, in TestEntitlementInitialization, like in #127814, and call that in BootstrapForTesting.

My idea was then to use it in TestEntitlementInitialization, and call that from BootstrapForTesting. See #127814. I'm open to moving that to BootstrapForTesting (which likely means getting rid of TestEntitlementInitialization), but having a separate class parallel to EntitlementInitialization makes it cleaner IMO.

[jdconrad]

I will close this based on @ldematte's feedback.