[10-10CG] Move auth_token_path to config

[coope93]

Summary

• This work is behind a feature toggle (flipper): YES
• Moving the auth_token_path from vets-api const to a config due to the possibility of future changes to it.
• 1010 Health Apps
• this is behind the cg1010_oauth_2_enabled flipper toggle

Related issue(s)

• [BE] 10-10CG - OAuth2.0: Submit forms using new auth flow in Production va.gov-team#90419
• Add configs to vsp manifest: https://github.com/department-of-veterans-affairs/vsp-infra-application-manifests/pull/3281

Testing done

• New code is covered by unit tests

What areas of the site does it impact?

10-10CG

Acceptance criteria

• I fixed|updated|added unit tests and integration tests for each feature (if applicable).
• No error nor warning in the console.
• Events are being sent to the appropriate logging solution
• Documentation has been updated (link to documentation)
• No sensitive information (i.e. PII/credentials/internal URLs/etc.) is captured in logging, hardcoded, or specs
• Feature/bug has a monitor built into Datadog (if applicable)
• If app impacted requires authentication, did you login to a local build and verify all authenticated routes work as expected
• I added a screenshot of the developed feature

[JoshingYou1]

LGTM! Nice work Brandon 😄

[github-actions]

Backend-review-group approval confirmed.