update hack/generate-kind-config.sh to handle multiple mirrors

[briandealwis]

Description

Related to: #5231

Update the hack/generate-kind-config.sh to handle multiple mirrors. The containerd docs notes:

The endpoint is a list that can contain multiple image registry URLs split by commas.

The resulting output:

$ docker system info
...
Registry Mirrors:
  https://registry-1.travis-ci.com/
  https://mirror.gcr.io/
 Live Restore Enabled: false
...
apiVersion: kind.x-k8s.io/v1alpha4
kind: Cluster
containerdConfigPatches:
- |-
  [plugins."io.containerd.grpc.v1.cri".registry.mirrors."docker.io"]
    endpoint = ["https://registry-1.travis-ci.com/","https://mirror.gcr.io/"]
Creating cluster "kind" ...
 • Ensuring node image (kindest/node:v1.20.2) 🖼  ...
 ✓ Ensuring node image (kindest/node:v1.20.2) 🖼
 • Preparing nodes 📦   ...
 ✓ Preparing nodes 📦 
 • Writing configuration 📜  ...
 ✓ Writing configuration 📜
 • Starting control-plane 🕹️  ...
 ✓ Starting control-plane 🕹️
 • Installing CNI 🔌  ...
 ✓ Installing CNI 🔌
 • Installing StorageClass 💾  ...
 ✓ Installing StorageClass 💾
Set kubectl context to "kind-kind"
You can now use your cluster with:
kubectl cluster-info --context kind-kind
Thanks for using kind! 😊

[briandealwis]

🎉 Hurray! Green builds from kind! 🎉

[nkubala]

🎩

[codecov]

Codecov Report

Merging #5977 (e8a37eb) into master (23098f5) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #5977   +/-   ##
=======================================
  Coverage   70.67%   70.68%           
=======================================
  Files         459      459           
  Lines       17597    17659   +62     
=======================================
+ Hits        12437    12482   +45     
- Misses       4239     4253   +14     
- Partials      921      924    +3     

Impacted Files	Coverage Δ
cmd/skaffold/app/cmd/inspect_profiles.go	63.15% <0.00%> (-29.15%)	⬇️
cmd/skaffold/app/cmd/inspect_modules.go	62.50% <0.00%> (-25.00%)	⬇️
pkg/skaffold/inspect/modules/list.go	83.33% <0.00%> (-16.67%)	⬇️
cmd/skaffold/app/cmd/inspect_build_env.go	58.21% <0.00%> (-1.23%)	⬇️
pkg/skaffold/parser/config.go	78.10% <0.00%> (-0.88%)	⬇️
pkg/skaffold/parser/types.go	100.00% <0.00%> (ø)
pkg/skaffold/inspect/types.go	100.00% <0.00%> (ø)
cmd/skaffold/app/cmd/inspect.go	100.00% <0.00%> (ø)
pkg/skaffold/inspect/buildEnv/list.go	100.00% <0.00%> (ø)
pkg/skaffold/schema/latest/v1/config.go	58.82% <0.00%> (ø)
... and 5 more

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