feat(core): Introduce ERS mode, ability to connect to remote ERS

[elizabethhealy]

Proposed Changes

• ERS mode to run an ERS on its own
• Ability to connect to a remote ers:
  • sdk config updated to include connection params: endpoint, plaintext, insecure

End result for configs: if running in core more you need to provide a sdk_config since an ERS connection is needed for authorization, ability to run in entityresolution mode, ability to configure core and ers connections with sdk_config (plaintext, insecure, endnpoint)

Checklist

• I have added or updated unit tests
• I have added or updated integration tests (if appropriate)
• I have added or updated documentation

Testing Instructions

[elizabethhealy]

xtest is failing because it calls a reusable workflow in this repo on the main branch. when running against an xtest branch that calls the reusable workflow from this branch (which has been updated) it passes https://github.com/opentdf/platform/actions/runs/12015619289/job/33494067371
so xtest will pass again officially when this is merged to main