[webservice] Add proposal state check

Description

This PR addresses https://git.xfel.eu/calibration/planning/-/issues/109 where it's described that we want to run closed proposals on the regular partitions, rather than blocking ongoing proposals.

How Has This Been Tested?

Unit test + test on max-exfl017:

proposal on test_metadata	action	expected partition	proposal status	passed	log
p900113	correct	exfel	FR	✓	2022-02-21 16:50:09,987 - root - DEBUG - [webservice.py:663] Using exfel for 900113 because FR
p900113	dark	exfel	FR	✓	2022-02-21 16:50:59,235 - root - DEBUG - [webservice.py:663] Using exfel for 900113 because FR
p900214	correct	upex-middle	A	✓	2022-02-21 16:52:13,047 - root - DEBUG - [webservice.py:663] Using exfel for 900214 because A
p900214	dark	upex-high	A	✓	2022-02-21 16:50:47,630 - root - DEBUG - [webservice.py:663] Using exfel for 900214 because A

Relevant Documents (optional)

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I added tests where appropriate.

Reviewers

@calibration