Merge workflow setup-new-repo.yml into main branch to be able to test

[hdamker]

What type of PR is this?

Add one of the following kinds:

• enhancement/feature

What this PR does / why we need it:

Adding the setup-new-repo.yml to main as it has to run once within main before it can be tested within a branch. Further test and iterations can then be done also in a test branch.

Which issue(s) this PR fixes:

Fixes # none completely, one step of #12

Special notes for reviewers:

See the single commits to review the changes compared to the workflow which was tested within Template_API_Repository

Additional documentation

Prerequisites already prepared:

• A GitHub environment named repo-setup must exist.
  • The environment must contain a secret GH_REPO_CREATE_TOKEN.
  • This token must be a fine-grained personal access token (FGPAT) with the following:
    • Repository access: Allow access to the template repo and target org repos.
    • Permissions:
    - Contents: Read and write
    - Issues: Read and write
    - Metadata: Read-only
    - Administration: Read and write (for repo settings, team setup)