Add environment to custom JWT claims [RUN ALL RSPEC] [RUN AS-IF-FOSS]

What does this MR do?

Adds environment and environment_protected fields to the JWT passed to CI builds.

This allows Vault users to restrict credentials to individual environments that are deployed from the same branch (previously dedicated branches were required per-environment).

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry (behind feature flag)
• [-] Documentation (if required) (behind feature flag)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Related to #294440 (closed)