[mysql_controller] simplify mysql controller with indexer and ListOptions

[nakamasato]

Changes

• Use client.MatchingFields

  r.List(ctx, mysqlUserList, client.MatchingFields{"spec.mysqlName": mysql.Name})`

• Set Index for spec.mysqlName in main.go and mysql_controller_test.go

      cache := mgr.GetCache()
      indexFunc := func(obj client.Object) []string {
    	  return []string{obj.(*mysqlv1alpha1.MySQLUser).Spec.MysqlName}
      }
      if err := cache.IndexField(context.TODO(), &mysqlv1alpha1.MySQLUser{}, "spec.mysqlName", indexFunc); err != nil {
    	  panic(err)
      }

• Use actions/setup-go@v3 instead of v2 in GitHub Actions

• Change the install command from go get to go install in Makefile

• Upgrade kustomize to v4.5.2 to fix (ref: Support go 1.16 module aware install with version kubernetes-sigs/kustomize#3618)

  go: creating new go.mod: module tmp
  Downloading sigs.k8s.io/kustomize/kustomize/v3@v3.8.7
  go: sigs.k8s.io/kustomize/kustomize/v3@v3.8.7 (in sigs.k8s.io/kustomize/kustomize/v3@v3.8.7):
          The go.mod file for the module providing named packages contains one or
          more exclude directives. It must not contain directives that would cause
          it to be interpreted differently than if it were the main module.
  make: *** [kustomize] Error 1
  

Indexing

Indexes may be added to caches using a FieldIndexer. This allows you to easily and efficiently look up objects with certain properties. You can then make use of the index by specifying a field selector on calls to List on the Reader corresponding to the given Cache.

• https://pkg.go.dev/sigs.k8s.io/controller-runtime@v0.10.0/pkg/client#hdr-Indexing
• https://github.com/kubernetes-sigs/controller-runtime/blob/master/pkg/client/example_test.go
• https://stackoverflow.com/questions/57083221/list-custom-resources-from-caching-client-with-custom-fieldselector
• https://pkg.go.dev/sigs.k8s.io/controller-runtime/pkg/client#example-FieldIndexer-SecretName

[codecov]

Codecov Report

Merging #95 (2379e2a) into main (ca00f7d) will decrease coverage by 0.33%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##             main      #95      +/-   ##
==========================================
- Coverage   77.14%   76.81%   -0.34%     
==========================================
  Files           5        5              
  Lines         210      207       -3     
==========================================
- Hits          162      159       -3     
  Misses         31       31              
  Partials       17       17              

Impacted Files	Coverage Δ
controllers/mysql_controller.go	77.41% <50.00%> (-2.00%)	⬇️

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