Confirm drawn overlay correct

[DominicOram]

When we draw the grid on the OAV we want the centre of each box to indicate where data was taken. When we supply the grid to the fast motion control program we supply the first point to be taken and the subsequent steps. We need to make sure these are as expected.

Acceptance Criteria

• We reason about the overlay and see if we think it is correct
• We write a test_grid_scan plan that we can a single 2D scan against a foil and confirm positions

[DominicOram]

From looking at the code I think the drawing is wrong, we use upper_left for both the motion controller start position (which defines the first centre) and the value in ispyb (which defines the upper left pixel to draw e.g. the upper left of the first box)

[DominicOram]

With above fix, confirmed at https://ispyb.diamond.ac.uk/dc/visit/cm33866-3/id/10979217. This was done using the calibrate_grids branch that's in prod. To finish off this ticket:

• Fix the above properly
• Get the calibrate code tidied up so that we can use it again if required

[DominicOram]

In discussion with Neil decided to not tidy what we currently have for calibration and instead redo it in DiamondLightSource/mx-bluesky#352