mergify: add backport strategy - backport PR#3849 to 0.44

[tzemanovic]

Describe your changes

Checklist before merging

• If this PR has some consensus breaking changes, I added the corresponding breaking:: labels
  • This will require 2 reviewers to approve the changes
• If this PR requires changes to the docs or specs, a corresponding PR is opened in the namada-docs repo
  • Relevant PR if applies:
• If this PR affects services such as namada-indexer or namada-masp-indexer, a corresponding PR is opened in that repo
  • Relevant PR if applies:

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.03%. Comparing base (e1983f2) to head (0eecd3b).
Report is 4 commits behind head on 0.44.0.

Additional details and impacted files

@@           Coverage Diff           @@
##           0.44.0    #3865   +/-   ##
=======================================
  Coverage   73.03%   73.03%           
=======================================
  Files         340      340           
  Lines      104816   104816           
=======================================
  Hits        76552    76552           
  Misses      28264    28264           

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