632 get flux from pv

[noemifrisina]

Fixes #632

Link to dodal PR (if required): #113

To test:

1. Check that all tests still pass

[DominicOram]

Good work, thank you. The test is failing because you need to patch the device in test_when_blueskyrunner_initiated_then_plans_are_setup_and_devices_connected, can you please add it in. We should add it in to S03 though but we can merge this without doing so

[DominicOram]

Great, thank you!

[DominicOram]

Must: You need to patch the Device, not teh function. I've fixed it :)

[codecov]

Codecov Report

Merging #785 (52ed1b4) into main (0b83859) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #785      +/-   ##
==========================================
+ Coverage   93.25%   93.26%   +0.01%     
==========================================
  Files          37       37              
  Lines        1854     1857       +3     
==========================================
+ Hits         1729     1732       +3     
  Misses        125      125              

Impacted Files	Coverage Δ
...rc/artemis/experiment_plans/fast_grid_scan_plan.py	93.50% <100.00%> (+0.12%)	⬆️
...emis/external_interaction/ispyb/ispyb_dataclass.py	98.18% <100.00%> (ø)

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