fix(kuma-dp) match gateway cluster names in the hijacker

[jpeach]

Summary

Gateway generates cluster names differently than the outbound proxy
generator, so each the metrics hijacker how to deal with both cluster
name conventions.

Full changelog

N/A

Issues resolved

N/A

Documentation

N/A

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 #3106 (c8db95c) into master (ba93741) will increase coverage by 0.03%.
The diff coverage is 81.81%.

@@            Coverage Diff             @@
##           master    #3106      +/-   ##
==========================================
+ Coverage   52.33%   52.37%   +0.03%     
==========================================
  Files         923      923              
  Lines       53578    53573       -5     
==========================================
+ Hits        28040    28057      +17     
+ Misses      23301    23289      -12     
+ Partials     2237     2227      -10     

Impacted Files	Coverage Δ
app/kuma-dp/pkg/dataplane/metrics/merge.go	87.83% <81.81%> (+2.21%)	⬆️
pkg/xds/generator/direct_access_proxy_generator.go	82.75% <0.00%> (-1.15%)	⬇️
pkg/plugins/resources/postgres/store.go	75.52% <0.00%> (+0.84%)	⬆️
api/observability/v1/mads.pb.go	35.56% <0.00%> (+1.03%)	⬆️
pkg/core/managers/apis/mesh/mesh_manager.go	49.38% <0.00%> (+2.46%)	⬆️
pkg/mads/v1/client/client.go	43.75% <0.00%> (+2.50%)	⬆️
pkg/core/resources/manager/cache.go	85.71% <0.00%> (+2.59%)	⬆️
pkg/defaults/mesh/mesh.go	77.77% <0.00%> (+3.70%)	⬆️
pkg/defaults/components.go	92.15% <0.00%> (+3.92%)	⬆️
pkg/defaults/mesh/signing_key.go	76.47% <0.00%> (+11.76%)	⬆️
... and 1 more

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[michaelbeaumont]

LGTM