do not allow creation of merge requests for pipline-branches

Description

if you've some runner-connected branches like

production/client_a
production/client_b
production/client_c
production/…

and the pipeline will deploy client_c if something is pushed to production/client_c - then you wont have a „Create Merge Request“ button to prevent from acciendtially creating merge request. imagine two developer - a is pushing a branch to create an merge request an b is pushing to production/client_c slightly after a - so a expects his branch to be in the merge request - but accidentially its not …

Proposal

Links / references

Documentation blurb

similar to protected branches, it should be possible to mark branches as „do not create merge-request for …“