[MOO-2286] : Release script fixes for Docs and changelog-MiN-11-12

[MendixMobile]

In this PR -

• removed previous sync file removal logic
• Added sync logic to sync the mendixmobile/docs fork with upstream
• Added new secret - MENDIX_MOBILE_DOCS_PR_GITHUB_PAT in MiN repo and used it in the script which has more access
• Added the logic to raise changelog PR against the correct base branch from which MiN is released and not always the main branch