batches: prototype of repo tag support and search

Created by: LawnGnome

Assuming we wanted to go ahead with this (which would be a product decision, obviously), we would need to give this PR a decent amount of love before it's reviewable. Off the top of my head:

• Unit tests
• Storybook tests
• Like, all the tests
• Code and GraphQL documentation
• Refactor the bits of batch change text search I just straight copy/pasted out of the enterprise codebase into a package somewhere in lib or internal
• Proper pagination support for tags/labels in the UI, since it's all just hardcoded right now
• A decision on what to call these (tags or labels)
• Design review, because those tags are ugly
• A decision on what to do about filter syntax in changeset search
• Remove whatever debugging code I left in here
• Have someone who actually knows RxJS wire up the updating code for repo tags properly, instead of my "let's make it a promise and pretend RxJS doesn't exist!" approach
• Documentation, including an example of how to wire this up to a third party source of truth