Allow disabling "remote: Create merge request for branch" message

Description

The line that gives you a link to a MR when pushing to GitLab confuses people and scripts.

It should be possible to turn this off on the project level.

Proposal

A simple checkbox to turn off this feature on the project level.

The default value should be ON: the message is displayed.

Links / references

Original issue

Hi,

after upgrading to 8.11 the following message appears on command line when pushing to a feature branch:

[stefan@arch-64-platon mse-utils]$ git push origin feature/gitlab-ci 
Total 0 (delta 0), reused 0 (delta 0)
remote: 
remote: Create merge request for feature/gitlab-ci:
remote:   https://gitlab.domain.de/merge_requests/new?merge_request%5Bsource_branch%5D=feature%2Fgitlab-ci
remote: 
To gitlab.domain.de:user/repo.git

This message is very annoying (the GitLab frontend will also show a message to create a new merge request). How can this warning be disabled (or better: turn it off by default, as the same functionality is provided by the GitLab frontend).

It was introduced with gitlab-shell!77 (merged).

Thanks in advance :)