Resolve "Add `meltano run [<plugin>...]` to run arbitrary plugins in a pipeline"

Merge Request Checklist

• Link to an issue
• Include the proposed fix or feature
• Include and update tests for the modified code
• Include a documentation change
• Add a CHANGELOG.md entry in the Unreleased section for any user-facing changes
• Mention or assign a maintainer

Burn down list

• tests
  • ELBContext and friends
  • Switch ExtractLoad tests to use ELBContext
  • cli tests
    • parsers
    • ExtractLoadBlock runs successful
    • PluginCommand (dbt) runs successful
    • "complex" run test e.g. meltano run tap target dbt:run
    • tap/target failure scenarios (mirroring test_elt tests)
      • tap fails first
      • target fails before tap finishes
      • target fails after tap finishes
      • both tap and target fail
    • Ye'olde tap line_length_limit_error handling test
    • PluginCommand (dbt) failures
    • output handling/capture verification
• job/sync support
  • refresh_full, force, etc ? (got ok from @aaronsteers to punt on these if we're pressed for time)
• clean up ELBContext use
• clean up/consistent log use
• docs

Closes #2301 (closed)