Declarative configuration files for configuring AutoMerge and auto-generating documentation

[ericphanson]

Transferred from JuliaRegistries/General#36875 (comment)

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One option would be to auto-generate the docs for General as well. E.g. use Documenter instead of having a long README. And in the Documenter docs, we'd auto-generate the list of automerge guidelines.

If we did want to go this route, we could maybe do something so that you don't need to repeat/sync-up settings between AutoMerge.run to actually run the automerge and between the docs. It would be cool to have all checks be individually configurable, maybe with Preferences.jl, and then have a docs script that reads those preferences and generates the appropriate docs for the registry (for General or for any other registry). And of course AutoMerge.run would use those preferences too, to choose which checks to apply.

I think the other benefit of Preferences is that we wouldn't need to have a zillion keyword arguments to AutoMerge.run or thread them through everywhere, since we could just read them in the function that needs to decide which checks to apply.

[MarkNahabedian]

Issues like #438, what suggest that there are workflows that use RegistryCI.AutoMerge but want to control various parameters and even which guidelines are checked rfom their registration workflows.