Add rubocop binstub, simplify configuration

[mjankowski]

Series of related changes:

• Add bin/rubocop binstub for rubocop and configure CI linter call to use it
• Re-organize the top-level .rubocop.yml file to ONLY declare the AllCops config and allow other files to come in via inherit_from config
• Move all the previous per-department configuration into one file per department config in a .rubocop dir, doing some yaml sort/cleanup while moving
• Once over on all the comments ... most of these seemed sort of pointless to me, basically re-stating what the rule does. I preserved the ones where in my judgement it was not totally obvious why the config was there.
• Move the config for the linters which are defined by the repo (ie, not from external gems) to a custom.yml file (this is just the middledot thing now)
• Add a "strict" config which gets loaded AFTER the todo, ensuring its cops always run on all files

No rules or config are actually changed here, but I do want to continue to work through the _todo file and some of the top-level Exclude I've moved here.

Many of these ideas are inspired by this approach: https://evilmartians.com/chronicles/rubocoping-with-legacy-bring-your-ruby-code-up-to-standard

I have a WIP branch which does a version of the "start with standardrb ruleset and then override" described in that blog post, but wanted to start with just the config portion.

[mjankowski]

Added a few more ideas/commits here, updated description to reflect.

[github-actions]

This pull request has merge conflicts that must be resolved before it can be merged.

[github-actions]

This pull request has resolved merge conflicts and is ready for review.

[ClearlyClaire]

What is the benefit of adding a binstup for rubocop?

[mjankowski]

What is the benefit of adding a binstup for rubocop?

For the binstub aspect specifically here, motivation is some mix of:

• Regular justification for adding binstubs ... it's just a slightly shorter/elegant shortcut to launch commands wrapped in bundler env load - locally, on CI, etc
• If you have bin added to $PATH with a .git/safe approach, puts the commands in path as well
• Rails 7.2 generates rubocop and brakeman binstubs by default (hence Add binstub for brakeman #30493) so its in part an extraction from that other PR

Not earth shattering, just small improvement (we have bin/rails, bin/rspec, bin/rake, etc already)