Improve error message when input isn't declared in pipeline

[Mokshit06]

Currently, if you have a Runefile.yml that looks like

pipeline:
  some_input:
    capability: ...
    output: ...
  processing:
    inputs:
      - another_input

it will throw an error like IndexMap: key not found because another_input isn't declared in the pipeline.

I think it would be a better debugging experience if it would throw an error like 'another_input' was not found in the pipeline, but is being passed as an input to 'processing'.
This error is particularly confusing when it occurs due to a typo.

[Michael-F-Bryan]

Resolved by #322.