Add command to update legacy wins totals.

[elcct]

Description of change

This adds a command that will let us update legacy Export wins totals from given spreadsheet.

This PR also ensures that the totals will not be recalculated for legacy Export wins.

Checklist

• Has this branch been rebased on top of the current main branch?

  Explanation

  The branch should not be stale or have conflicts at the time reviews are requested.

• Is the CircleCI build passing?

General points

Other things to check

• Make sure fixtures/test_data.yaml is maintained when updating models
• Consider the admin site when making changes to models
• Use select-/prefetch-related field lists in views and search apps, and update them when fields are added
• Make sure the README is updated e.g. when adding new environment variables

See docs/CONTRIBUTING.md for more guidelines.

[dredmonds]

It looks okay this PR except a failing testing to be fix. https://app.circleci.com/pipelines/github/uktrade/data-hub-api/20826/workflows/16dcf988-ad96-48b0-934b-42bfdc5768b5/jobs/28819?utm_campaign=vcs-integration-link&utm_medium=referral&utm_source=github-checks-link&utm_content=summary

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.41%. Comparing base (392df95) to head (a4fee36).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5763   +/-   ##
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  Coverage   96.40%   96.41%           
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  Files        1026     1027    +1     
  Lines       24450    24472   +22     
  Branches     2213     2217    +4     
=======================================
+ Hits        23572    23594   +22     
  Misses        709      709           
  Partials      169      169           

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