Add patching script for CoC modifications

[tobie]

As discussed in #909, and requested in #851, we'd like to add a patch file for the CoC and a script to automate patching updates. Both should be versioned.

Pointers on best practices to do that are welcomed.

[ljharb]

Absent an exemplar to follow, I envision a custom script that works in this way:

1. the repo stores a SHA of the upstream CoC; a local patch file, and a local build output CoC file.
2. the script fetches the contents of the SHA, applies the patch file, and commits the result
3. we add a github action that fails if the script runs and produces a git diff

[Relequestual]

It looks like this issue has been on the agenda multiple times.
Could we get some expansion on what's required here? I'm not clear, even with the context of it blocking #851.

The Contributor Covenant CoC is updated VERY rarely. In the event it's updated, such as a major version, it doesn't feel likely that the patch would work. If there's a structural change, the diff isn't going to be applied well.

If the answer is, "OK, then we need a new patch at that point in time," I think that's OK, but it feels like overhead.

[ljharb]

Every time it's come up, the sense has seemed to be that we need #910 (comment) next.

[tobie]

@ljharb, I think Ben has a point: if we're blocking on a technical implementation that's currently for a one-line diff, maybe we should reconsider building tooling for this, and instead do it manually, at least for now.

[ljharb]

@tobie oh sure, i wasn't disagreeing with the point, i was just reiterating past consensus.