Polish transform branching

[lukesteensen]

The basic functionality was merged in #9169, but there's a bit we should still do to make it more solid:

• Replace fn named_outputs(&self) -> Vec<String> with something that more fully models outputs, including name, data type, and whether it is required to be read from. Then drive topology building more directly off of that type. (enhancement(topology): branching without defaults #10640)
• Revisit the design of the transform enum and traits to simplify and more directly model branching (done as part of enhancement(topology): run transforms concurrently #10265)
• Adjust the component spec to break out metrics by output (docs(internal docs): Update component spec for multiple outputs #10687)
• Add named outputs as structured data to cue docs and the website #10615
• Decide which other transforms should have additional outputs #10660
• Add support for testing them to unit tests (chore(unit tests): Leverage existing topology logic for unit test internals #10540)
• Update vector top for multiple outputs #10871
  • We should consider how vector tops TUI should be updated to deal with statistics for named outputs
• Ensure vector tap still works
  • That we can vector tap some_remap.dropped for just the dropped events or vector tap some_remap for the "default output". We should also be able to vector tap some_route.* to see all events.
  • vector tap functionality was verified against a local build of master (671109076). Here is the config used for testing. Checked the following behavior
    • Can tap the default output of a remap transform
    • Can tap the dropped output of a remap transform
    • Can tap each route of a route transform
    • Can tap a glob of outputs for remap and route
  • Will follow this up with adding unit tests. chore(api): Add unit tests for vector tap on multiple outputs #10972
• Update component instrumentation for multiple outputs #10832
• Structured error messages from VRL #10686

[wbew]

Closing this as all the associated tasks are complete.