Fix broken outputs from GSM actions

[DerTiedemann]

As you can see by the commit history - this was a ride which ultimately led me back to the toJSON workaround, in which usability suffers quite a bit. There has to be a better solution to this than just chaining actions together and glueing them togehter, but for now this is functional.

Here is an example workflow that works:

name: test

on:
  workflow_dispatch:

permissions:
  contents: read
  id-token: write

jobs:
  test-secret-fetch:
    name: load secrets
    runs-on: ubuntu-latest

    steps:
      - name: Load secrets
        id: load-secrets
        uses: bakdata/ci-templates/actions/gcp-gsm-load-secrets@tiedemann/gsm-object-outputs-fix
        with:
          gke-project-name: <redacted>
          workload-identity-provider: <redacted>
          gke-service-account: <redacted>
          secrets-to-inject: |-
             CRABBY_PATTY_FORMULA/1
      - name: test exported
        run: |
          echo "${{ fromJSON(steps.load-secrets.outputs.secret-json-string).CRABBY_PATTY_FORMULA }}" | rev

As you can see this is less then ideal but it works.
Just as a though, having 2 vanilla actions (gcp auth + gsm get secrets) might be a whole lot easier than rolling our own stuff. Maybe we just take the learnings and have sth simple.