Add POST configuration secrets endpoint

[dotNomad]

This PR adds a new API endpoint POST /api/configurations/$NAME/secrets that:

• takes an action and secret name similar to the POST files API
• returns a configDTO containing the projectDir, configuration, and configLocation for easy plug into our frontend store

Intent

Part of #2305

Type of Change

• • [ ] Bug Fix
• • [x] New Feature
• • [ ] Breaking Change
• • [ ] Documentation
• • [ ] Refactor
• • [ ] Tooling

Directions for Reviewers

Test out the new endpoint:

• testing the add and remove action
• testing in and out of multi-directory roots

http POST :9001/api/configurations/fastapi-simple-QSPH/secrets action=add secret=new http POST :9001/api/configurations/fastapi-simple-QSPH/secrets action=remove secret=new http POST :9001/api/configurations/fastapi-simple-QSPH/secrets action=remove secret=new dir==fastapi-simple http POST :9001/api/configurations/fastapi-simple-QSPH/secrets action=add secret=new dir==fastapi-simple