Change the `secrets` keyword to use CI_JOB_JWT_V2

Scope

This issue is part of a bigger development effort described in detail by its epic. The scope of this issue is to coordinate the work needed to move the secrets stanza over to the new CI_JOB_JWT_V2 predefined variable.

Proposal

Use the CI_JOB_JWT_V2 based on a new configuration value

Iterations

1. Implement the configuration, and set the default to be CI_JOB_JWT
   • create a deprecation notice
2. Change the default to CI_JOB_JWT_V2 in %15.0 and leave the configuration option
3. Update the documentation with the necessary changes to allow users to reconfigure their Authentication with Vault - #357624 (closed)

Current status! (as of the start of %14.10)

See #349110 (comment 874544155)