Simple way to view JSON schema for a plan

[callumforrester]

If I write a bluesky plan I may wish to write client code against its JSON schema, a simple tool to view said schema would be useful. Right now I would have to:

1. Have a blueapi server that loaded the plan into its context
2. Curl <server>/plans/<plan name> and dig the schema out of the response body

Just being able to run a simple command like blueapi plan schema my_file.py::my_plan would be helpful

Acceptance Criteria

• TBD