Force clients to provide the current index to run `produce` or
`runAnalysis`. Requests that do not provide the correct index return an
IndexError object.
This commit introduces the concept of `Component` to a pipeline step.
This, in turn, can be used by clients to figure out which artifacts are
produced by which revng component.
Additionally, this commit overhauls the `revng daemon-self-test`
command, renaming it to `revng graphql` and adding extra flexibility.
Giacomo Vercesi