File tree diff: allow ignoring files

[stsewd]

What's the problem this feature will solve?

With the new FTD feature, there may be some files that always get changes, or that aren't really relevant for the diff.

Describe the solution you'd like

Users should have an option to ignore these files from being considered in the diff, similar to what we have in our search config https://docs.readthedocs.io/en/stable/config-file/v2.html#search-ignore.

Alternative solutions

Just deal with the files, maybe just have a nice filtering UI.

Additional context

#11646

[humitos]

maybe just have a nice filtering UI

This is an interesting thing to consider. We can always calculate the diff of all these files, but not show them in the UI under the list of files changed. That way, if this list of ignored files change, we don't need to re-build all these versions.