fix(import): import flags with complex metadata

[erka]

This pull request includes several changes to the internal/ext package to enhance the encoding and importing functionalities.

• yaml.v3 is used as import encoder. It returns map[string]any instead of map[any]any in jaml.v2.
• fix the issue with importing json backups generated by flipt export -o file.json

closes #3635
closes #3636

[codecov]

Codecov Report

Attention: Patch coverage is 55.00000% with 9 lines in your changes missing coverage. Please review.

Project coverage is 64.31%. Comparing base (1f6255d) to head (7fa170c).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/ext/importer.go	52.63%	6 Missing and 3 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3639   +/-   ##
=======================================
  Coverage   64.31%   64.31%           
=======================================
  Files         170      170           
  Lines       17020    17019    -1     
=======================================
  Hits        10946    10946           
+ Misses       5395     5392    -3     
- Partials      679      681    +2     

Flag	Coverage Δ
unittests	64.31% <55.00%> (+<0.01%)	⬆️

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[markphelps]

thank yoU!!