Move CentreEllipseMethod to a more common location

[noemifrisina]

Needed for i19-bluesky#122

Instructions to reviewer on how to test:

1. Run tests
2. Check that all code using this device has been updated

Checks for reviewer

• Would the PR title make sense to a scientist on a set of release notes
• If a new device has been added does it follow the standards
• If changing the API for a pre-existing device, ensure that any beamlines using this device have updated their Bluesky plans accordingly
• Have the connection tests for the relevant beamline(s) been run via dodal connect ${BEAMLINE}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.10%. Comparing base (7913c36) to head (233766f).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1942   +/-   ##
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  Coverage   99.09%   99.10%           
=======================================
  Files         317      317           
  Lines       11995    12000    +5     
=======================================
+ Hits        11887    11892    +5     
  Misses        108      108           

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[DominicOram]

Thanks, minor comment. Could you also add a test that explicitly checks that if you specify a large ROI it gives you the full image? It may be covered by test_get_roi_creates_correct_image_array, if it is then just a comment on one of those cases would be good.

[DominicOram]

Nit:

Suggested change

	LOGGER.info(f"Beam centre founf at ({roi_centre_x}, {roi_centre_y})")
	LOGGER.info(f"Beam centre found at ({roi_centre_x}, {roi_centre_y})")

[DominicOram]

Also, this is the centre in the ROI co-ordinates, I think the full image co-ordinates would be more expected (or specify in the log that they're ROI)