getStreamMetrics() station input is not documented fully

[mhearne-usgs]

Describe the bug
Here:
https://github.com/usgs/groundmotion-processing/blob/main/src/gmprocess/io/asdf/stream_workspace.py#L1204

station is meant to be the "S.C.L" part of "N.S.C.L" (Network-Station-Channel-Location), where in other methods (getStreams()) station is the full NSCL code.

To Reproduce
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Expected behavior
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Environmnet (please complete the following information):

• OS: [e.g. macOS]
• Python Version [e.g. 3.6]
• Libcomcat Version [e.g. 1.0]
• Numpy Version [e.g. 1.17]

Additional context
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