ObservationModule observation dictionary should accept list of detectors

[york-stsci]

Currently when setting up an observation parameter dictionary for an ObservationModule, there is an expected integer parameter 'detectors', which specifies how many detectors should be modeled in each observation. This both gives very little flexibility in terms of which detectors to include, and also means that if you want, for example, Roman WFI SCA12, and only that detector, you have to specify 'detector': 12 in the dictionary and have STIPS calculate SCA01-SCA12, thus wasting more than 90% of its calculation time.

Instead, detectors should take one of the following:

• a string (e.g. 'SCA01') specifying a single detector
• an integer (as currently) asking for the first N detectors
• a list of strings (e.g. ['SCA01', 'SCA05', 'SCA13', 'SCA15']) allowing for multiple detectors that aren't necessarily in order.