feat(gateway): add loadBalancerIP to MeshGatewayInstance

[michaelbeaumont]

Summary

As discussed in #4075 (comment), this is necessary for Azure Load Balancers with static IPs.

[codecov-commenter]

Codecov Report

Merging #4519 (5f178a7) into master (cb04bdd) will decrease coverage by 0.01%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #4519      +/-   ##
==========================================
- Coverage   47.06%   47.05%   -0.02%     
==========================================
  Files         676      676              
  Lines       45064    45075      +11     
==========================================
- Hits        21210    21208       -2     
- Misses      21992    22006      +14     
+ Partials     1862     1861       -1     

Impacted Files	Coverage Δ
...s/k8s/native/api/v1alpha1/zz_generated.deepcopy.go	30.78% <0.00%> (-0.24%)	⬇️
...ime/k8s/controllers/gateway_instance_controller.go	0.00% <0.00%> (ø)
pkg/api-server/server.go	74.58% <0.00%> (-2.09%)	⬇️
pkg/plugins/leader/postgres/leader_elector.go	89.36% <0.00%> (+6.38%)	⬆️

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