New OIDC auth method

[rgharris]

This depends on yet to be released API changes and is not ready to be merged yet. This has been tested with the unpublished API changes via the new doppler-api-domain option.

Release Note: Add OIDC support to the Github Secrets Fetch Action. This allows the action to retrieve secrets from a Doppler service account by authenticating via identity auth.

Closes ENG-8513

Example usages:

name: Doppler secrets from outputs

on: [push]

jobs:
  secrets-fetch-sa-oidc:
    runs-on: ubuntu-latest
    permissions:
      id-token: write # required for obtaining the OIDC JWT from Github
    steps:
    - uses: dopplerhq/secrets-fetch-action@rgharris/oidc # update to use @v1.3.0 after launch
      id: doppler
      with:
        auth-method: oidc        
        doppler-identity-id: 78efd55a-a93c-4415-8078-7db6a588ba73
        doppler-project: example-project
        doppler-config: dev
        doppler-api-domain: your-custom-local-domain # for local testing only
    - run: echo "DOPPLER_PROJECT is ${{ steps.doppler.outputs.DOPPLER_PROJECT }} (Doppler meta environment variables are unmasked)"
    - run: echo "ANEWONE is ${{ steps.doppler.outputs.ANEWONE }} (secret masked output)"

  secrets-fetch-sa-token:
    runs-on: ubuntu-latest
    steps:
    - uses: dopplerhq/secrets-fetch-action@rgharris/oidc # update to use @v1.3.0 after launch
      id: doppler
      with:
        doppler-token: ${{ secrets.DOPPLER_SA_TOKEN }}
        doppler-project: example-project
        doppler-config: dev
        doppler-api-domain: your-custom-local-domain # for local testing only
    - run: echo "DOPPLER_PROJECT is ${{ steps.doppler.outputs.DOPPLER_PROJECT }} (Doppler meta environment variables are unmasked)"
    - run: echo "ANEWONE is ${{ steps.doppler.outputs.ANEWONE }} (secret masked output)"

  secrets-fetch-service-token:
    runs-on: ubuntu-latest
    steps:
    - uses: dopplerhq/secrets-fetch-action@rgharris/oidc # update to use @v1.3.0 after launch
      id: doppler
      with:
        doppler-token: ${{ secrets.DOPPLER_SERVICE_TOKEN }}
        doppler-api-domain: your-custom-local-domain # for local testing only
    - run: echo "DOPPLER_PROJECT is ${{ steps.doppler.outputs.DOPPLER_PROJECT }} (Doppler meta environment variables are unmasked)"
    - run: echo "ANEWONE is ${{ steps.doppler.outputs.ANEWONE }} (secret masked output)"