ci: check if a PR can be backported

[tzemanovic]

Describe your changes

A new CI step "PR: can-backport" checks API compatibility of the libs against the last release (v0.47.2) and if there are API breaking changes requiring major release it will label the PR with "breaking:api", otherwise it will label it to "backport-libs-0.47" for a minor release.

Note that currently the semver-checks step fails because of couple build issues with various feature flags in libs-v0.47.2 that are fixed in here in the last 3 commits.

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[bot]]

Codecov Report

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

Project coverage is 74.52%. Comparing base (94d3a8e) to head (d0a5759). Report is 13 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4401   +/-   ##
=======================================
  Coverage   74.52%   74.52%           
=======================================
  Files         339      339           
  Lines      110504   110504           
=======================================
  Hits        82358    82358           
  Misses      28146    28146           

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