option to not push new commits on the main branch

[kevgo]

Extracted from #2223 (comment):

When the protected-main-branch option is set,

git-town/features/sync/current_branch/feature_branch/rebase_sync_strategy/sync_current_feature_branch_using_rebase.feature

Line 20 in 5ef3afa

| | git push |

should not happen. Instead, if it finds an unpushed commit on main, it should print an error notifying the user that there is an unpushed commit on main.

[ruudk]

Would this be something for V10 as well 🙏 ?

[kevgo]

This ticket is more about adding documentation for an edge case that people might run into if they don't follow their development workflow. I don't consider it critical so it is rather low on the list right now.