Merge details no longer shows "# commits behind"
### Summary
It is currently possible to merge into target branch without the knowledge, that it is behind and/or ahead of the target.
### Steps to reproduce
- Create a MR
- Add changes or files
- Let a Pipeline Run or Fail
### What is the current *bug* behavior?
MR is marked ready without the merge button, but is showing the commits behind information.

MR is marked ready with the merge button, but the MR is 100+ commits behind without showing it.

### What is the expected *correct* behavior?
- The ready status should only be shown if the merge button is shown
- Behind and Ahead target branch should always be shown if it is not 0.
### Details of package version
Gitlab Omnibus 15.1.2
### Proposal
Add `Commits behind...` info to widget:
```
[x] Delete source branch [ ] Edit commit message
The source branch is 59 commits behind the target branch • 2 commits and 1 merge commit will be added to master
[Merge]
```
issue