[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:

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