[WIP] Add registerRouteHandlersByTag function for operation tags

[Copilot]

Thanks for asking me to work on this. I will get started on it and keep this PR's description up to date as I form a plan and make progress.

Original prompt

In /packages/openapi-typescript-server/src/cli /generate.ts, codegen a new function called "registerRouteHandlersByTag".

The first argument should accept a string const union of all tags from all operations provided in the given open API spec. It should include a null tag which references untagged operations.The generated code shuld look a lot like the current registerRouteHandlers function, but it should only write operations to the interface that are associated with argument tag.

The goal is that callers can provide an implementation of the interface

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