#818 fix fgs plan system tests

[d-perl]

Starts but doesn't finish #818
Requires https://gitlab.diamond.ac.uk/controls/support/bl03s-builder/-/merge_requests/5 and DiamondLightSource/dodal#371

While we're at it, this would be good too:
https://gitlab.diamond.ac.uk/controls/python3/s03_utils/-/merge_requests/14

To test:

1. Build S03 with updated BL03S-BUILDER (note, you will need to change the install location in the BL03S-BUILDER Dockerfile if you aren't building it in /dls_sw/work/${EPICS_VERSION}/support/BL03S-BUILDER)
2. Confirm system tests in test_fgs_plan.py pass

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.51%. Comparing base (e3b7353) to head (cdff213).
Report is 206 commits behind head on main.

❗ Current head cdff213 differs from pull request most recent head 61c95b7. Consider uploading reports for the commit 61c95b7 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #944      +/-   ##
==========================================
+ Coverage   92.96%   93.51%   +0.54%     
==========================================
  Files          69       54      -15     
  Lines        3413     2590     -823     
==========================================
- Hits         3173     2422     -751     
+ Misses        240      168      -72     

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[DominicOram]

Confirmed that with the latest S03 these tests are more reliable than before. more effort needed to get them fully passing but moving that into later issues