Github action: create version number without manual input

[grischperl]

Description

Create a Github action that triggers the whole release flow, which is reusable for other repositories. The version is not manually entered as input but instead automatically taken from the naming of the release branch from which the release is being created.

note: some work was done here already: EM and here as well: EPP

Acceptance

• Reusable for all repositories
  -> reusable script
• Uses the release branch name as the version input
  -> here
• Check that release can only be created from branches following the pattern release-x.y
  -> here
• Version input created by branch name (x.y from branch name, z from existing version +1)
• Check that version follows correct order
  (e.g. 1.0.1 already exists, validation prevents you from creating 0.0.5)
  • might not be needed if following the branch versioning