Khoward height max vertical velocity

[Katie-Howard]

Addresses #GitHubissuenum

This is a plugin to find the height at which a maximum occurs. This is for the Maximum vertical velocity workflow. We need to know the height at which the maximum occurs for our meteorologists to help them identify lee waves.

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 98.32%. Comparing base (84a8944) to head (9227556). Report is 18 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #2012 +/- ## ========================================== - Coverage 98.39% 98.32% -0.08% ========================================== Files 124 129 +5 Lines 12212 12592 +380 ========================================== + Hits 12016 12381 +365 - Misses 196 211 +15 ```

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[Katie-Howard]

Acceptance test data is here: https://github.com/metoppv/improver_test_data/pull/51

[Katie-Howard]

I have a notebook within information on the acceptance test data that can be accessed through /data/users/khoward/EPP_data/max_vertical_velocity/vertical_velocity.ipynb