✨ Add option to choose between `git rebase` or `git merge`

[candoumbe]

Is your feature request related to a problem? Please describe.
Some repositories require linear history (i.e. no merge commits) but the default implementation of both IGitFow.FinishHotfix and IGitFlow.FinishRelease use merge commands. This causes commits / PRs to be rejected

Describe the solution you'd like
Add new setting RequireLinearHistory to make the pipeline choose between rebase or `merge which value should be :

• true : only perform rebase commands
• false : only perform merge commands

By default RequireLinearHistory will be false.

Describe alternatives you've considered
N/A

Additional context
Add any other context or screenshots about the feature request here.