compare branches: show all option
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### Summary
Since the last(?) release comparing branches now doesn't show all changes, but splits it in pages of 20(?) results.

### Steps to reproduce
Compare two branches with a substantial enough difference.
### Example Project
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### What is the current *bug* behavior?
There is no "show all" button or option (not even a per_page query option)
### What is the expected *correct* behavior?
A way where i can load all the changes in a single page so i can ctrl+f filenames and keywords without having to repeat it for all of my 4 pages just to find something again.

### Relevant logs and/or screenshots
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### Output of checks
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#### Results of GitLab environment info
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#### Results of GitLab application Check
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### Possible fixes
1) a show all option
2) a way to show more per page
issue