feat(*) aggregate dp stats by type in MeshInsight

[bartsmykla]

Summary

Currently we are returning only stats (total/online/offline) without distinction for the dp types (standard/gateway), I added dataplanesByType property to MeshInsights where stats are aggregated by these types.

Full changelog

no changelog

Issues resolved

no issue resolved

Documentation

• Link to the website: docs(*) update api reference for aggregate stats kuma-website#570

Testing

• Unit tests
• E2E tests
• Manual testing on Universal
• Manual testing on Kubernetes

Backwards compatibility

• Add backport-to-stable label if the code is backwards compatible. Otherwise, list breaking changes.

[codecov-commenter]

Codecov Report

Merging #2999 (7d4b69d) into master (7e40b0f) will increase coverage by 0.06%.
The diff coverage is 56.36%.

@@            Coverage Diff             @@
##           master    #2999      +/-   ##
==========================================
+ Coverage   52.21%   52.28%   +0.06%     
==========================================
  Files         912      912              
  Lines       52736    52788      +52     
==========================================
+ Hits        27538    27599      +61     
+ Misses      23004    22994      -10     
- Partials     2194     2195       +1     

Impacted Files	Coverage Δ
api/mesh/v1alpha1/mesh_insight.pb.go	32.38% <42.85%> (+3.54%)	⬆️
pkg/insights/resyncer.go	69.75% <100.00%> (+1.90%)	⬆️
pkg/plugins/leader/postgres/leader_elector.go	93.61% <0.00%> (-4.26%)	⬇️
api/observability/v1/mads.pb.go	35.56% <0.00%> (+1.03%)	⬆️
pkg/xds/generator/direct_access_proxy_generator.go	83.90% <0.00%> (+1.14%)	⬆️
pkg/mads/v1/client/client.go	43.75% <0.00%> (+2.50%)	⬆️
pkg/core/resources/manager/cache.go	88.31% <0.00%> (+2.59%)	⬆️
pkg/mads/server/server.go	85.18% <0.00%> (+2.77%)	⬆️
... and 3 more

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