Track updates for validators

[Stefan-Ethernal]

Description

This PR introduces another field to the ValidatorSetDelta which allows us to track updates in ValidatorMetadata instances.

Changes include

• Bugfix (non-breaking change that solves an issue)
• Hotfix (change that solves an urgent issue, and requires immediate attention)
• New feature (non-breaking change that adds functionality)
• Breaking change (change that is not backwards-compatible and/or changes current functionality)

Checklist

• I have assigned this PR to myself
• I have added at least 1 reviewer
• I have added the relevant labels
• I have updated the official documentation
• I have added sufficient documentation in code

Testing

• I have tested this code with the official test suite
• I have tested this code manually

[codecov]

Codecov Report

Merging #939 (293b050) into feature/v3-parity (db63825) will increase coverage by 0.14%.
The diff coverage is 100.00%.

@@                  Coverage Diff                  @@
##           feature/v3-parity     #939      +/-   ##
=====================================================
+ Coverage              53.84%   53.99%   +0.14%     
=====================================================
  Files                    163      163              
  Lines                  21566    21586      +20     
=====================================================
+ Hits                   11613    11656      +43     
+ Misses                  9007     8989      -18     
+ Partials                 946      941       -5     

Impacted Files	Coverage Δ
consensus/polybft/extra.go	86.98% <100.00%> (+0.33%)	⬆️
consensus/polybft/validator_metadata.go	85.71% <100.00%> (+4.94%)	⬆️
network/server_discovery.go	85.09% <0.00%> (+10.55%)	⬆️

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[goran-ethernal]

Left a short comment, but in general looks good.