RELTEC-12262: refactor webhooks endpoint to vcs webhooks, support

[KRaffael]

different vcs systems during user validation

Description

Please include a summary of the changes and the related issue. Please also include relevant motivation and context. List any dependencies that are required for this change.

Fixes # (issue)

Checklist

• I have read the CONTRIBUTING.md
• I have made corresponding changes to the documentation
• My changes generate no lint errors
• I have added tests that prove my fix is effective or that my feature works
• New and existing tests pass locally with my changes
• Only MIT licensed or MIT license compatible dependencies are used (e.g.: Apache2 or BSD)
• The code contains no credentials, personalized data or company secrets