MOBT-661: Required changes for precipitation phase accumulations

[brhooper]

Related to: https://github.com/metoppv/mo-blue-team/issues/661, https://github.com/metoppv/mo-blue-team/issues/671 Acceptance test data: https://github.com/metoppv/improver_test_data/pull/48

Description This PR includes a few changes which are required for the work to produce precipitation phase accumulations over longer periods.

Included changes are as follows:

• Add option for 'realization' tie-breaking within ECC. This resolves ties within the dependence template by assigning values to the highest realization number.
• Factor out code which enables recycling realizations in the ECC dependence template.
• Create a CLI for the above recycling code to enable extending the realization dimension on phase probability cubes. This ensures realization recycling is done using a consistent method, which is important for precipitation phase accumulation diagnostics for reasons laid out in this comment (https://github.com/MetOffice/improver_aux/pull/420#issuecomment-2051865950).
• Make one of the checks in the combine plugin easier to pass - test will no longer fail if coordinates on input cubes differ in the var_name, except if the difference is on a threshold coordinate. This mirrors, and was necessitated by, the functionality of the MergeCubes plugin, which removes this attribute from coordinates.

Testing:

• [x] Ran tests and they passed OK
• [x] Added new tests for the new feature(s)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 98.41%. Comparing base (84a8944) to head (0bb5bae). Report is 18 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1997 +/- ## ========================================== + Coverage 98.39% 98.41% +0.01% ========================================== Files 124 124 Lines 12212 12346 +134 ========================================== + Hits 12016 12150 +134 Misses 196 196 ```

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