Annotate imported EndpointSlices with multicluster label

[vanekjar]

Related to #22

Mark imported endpoint slices with multicluster.kubernetes.io/service-name annotation to denote a source ServiceImport.

Imported ServiceImport looks like this after adding labels:

Name:         imported-20b6661q92-sks2f
Namespace:    my-namespace
Labels:       kubernetes.io/service-name=imported-20b6661q92
              multicluster.kubernetes.io/service-name=nginx

Following the MCS API spec.

Since a given ServiceImport may be backed by multiple EndpointSlices, a given EndpointSlice will reference its ServiceImport using the label multicluster.kubernetes.io/service-name similarly to how an EndpointSlice is associated with its Service in a single cluster.

https://github.com/kubernetes/enhancements/tree/master/keps/sig-multicluster/1645-multi-cluster-services-api#importing-services

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[codecov-commenter]

Codecov Report

Merging #56 (2a30a42) into main (8f8df95) will decrease coverage by 0.12%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main      #56      +/-   ##
==========================================
- Coverage   42.32%   42.20%   -0.13%     
==========================================
  Files           9        9              
  Lines         997     1000       +3     
==========================================
  Hits          422      422              
- Misses        560      563       +3     
  Partials       15       15              

Impacted Files	Coverage Δ
pkg/controllers/cloudmap_controller.go	0.00% <0.00%> (ø)

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