[FLINK-37669][HELM] Add Helm chart unit tests to flink kubernetes operator

[ChenYi015]

What is the purpose of the change

(For example: This pull request adds a new feature to periodically create and maintain savepoints through the FlinkDeployment custom resource.)

Add Helm chart unit tests to flink kubernetes operator, see helm-unittest.

Brief change log

• Reorganize the Helm chart directory
• Add Helm chart unit tests
• Update .helmignore to ingore helm unit test files

$ # Before
$ tree helm/flink-kubernetes-operator  
helm/flink-kubernetes-operator
├── Chart.yaml
├── conf
│   ├── flink-conf.yaml
│   ├── log4j-console.properties
│   └── log4j-operator.properties
├── crds
│   ├── flinkdeployments.flink.apache.org-v1.yml
│   ├── flinksessionjobs.flink.apache.org-v1.yml
│   └── flinkstatesnapshots.flink.apache.org-v1.yml
├── templates
│   ├── _helpers.tpl
│   ├── flink-operator.yaml
│   ├── rbac.yaml
│   ├── serviceaccount.yaml
│   └── webhook.yaml

$ # After
helm/flink-kubernetes-operator
├── Chart.yaml
├── conf
│   ├── flink-conf.yaml
│   ├── log4j-console.properties
│   └── log4j-operator.properties
├── crds
│   ├── flinkdeployments.flink.apache.org-v1.yml
│   ├── flinksessionjobs.flink.apache.org-v1.yml
│   └── flinkstatesnapshots.flink.apache.org-v1.yml
├── templates
│   ├── _helpers.tpl
│   ├── certmanager
│   │   ├── _helpers.tpl
│   │   ├── certificate.yaml
│   │   └── issuer.yaml
│   ├── controller
│   │   ├── _helpers.tpl
│   │   ├── configmap.yaml
│   │   └── deployment.yaml
│   ├── flink
│   │   ├── _helpers.tpl
│   │   ├── role.yaml
│   │   └── role_binding.yaml
│   ├── rbac
│   │   ├── _helpers.tpl
│   │   ├── cluster_role.yaml
│   │   ├── cluster_role_binding.yaml
│   │   ├── role.yaml
│   │   ├── role_binding.yaml
│   │   └── service_account.yaml
│   └── webhook
│       ├── _helpers.tpl
│       ├── mutating_webhook_configuration.yaml
│       ├── secret.yaml
│       ├── service.yaml
│       └── validating_webhook_configuration.yaml
├── tests
│   ├── certmanager
│   │   ├── certificate_test.yaml
│   │   └── issuer_test.yaml
│   ├── controller
│   │   ├── configmap_test.yaml
│   │   └── deployment_test.yaml
│   ├── flink
│   │   ├── role_binding_test.yaml
│   │   └── role_test.yaml
│   ├── rbac
│   │   ├── cluster_role_binding_test.yaml
│   │   ├── cluster_role_test.yaml
│   │   ├── role_binding_test.yaml
│   │   └── role_test.yaml
│   └── webhook
│       ├── mutating_webhook_configuration_test.yaml
│       ├── secret_test.yaml
│       ├── service_test.yaml
│       └── validating_webhook_configuratioin_test.yaml

Verifying this change

This change added tests and can be verified as follows:

$ helm plugin install https://github.com/helm-unittest/helm-unittest.git --version 0.8.1

$ helm unittest helm/flink-kubernetes-operator --file "tests/**/*_test.yaml" --strict --debug

### Chart [ flink-kubernetes-operator ] helm/flink-kubernetes-operator

 PASS  Test Cert Manager Certificate    helm/flink-kubernetes-operator/tests/certmanager/certificate_test.yaml
 PASS  Test Cert Manager Issuer helm/flink-kubernetes-operator/tests/certmanager/issuer_test.yaml
 PASS  Test ConfigMap   helm/flink-kubernetes-operator/tests/controller/configmap_test.yaml
 PASS  Test Deployment  helm/flink-kubernetes-operator/tests/controller/deployment_test.yaml
 PASS  Test Flink Job RoleBinding       helm/flink-kubernetes-operator/tests/flink/role_binding_test.yaml
 PASS  Test Flink Job Role      helm/flink-kubernetes-operator/tests/flink/role_test.yaml
 PASS  Test Operator ClusterRoleBinding helm/flink-kubernetes-operator/tests/rbac/cluster_role_binding_test.yaml
 PASS  Test Operator ClusterRole        helm/flink-kubernetes-operator/tests/rbac/cluster_role_test.yaml
 PASS  Test Operator RoleBinding        helm/flink-kubernetes-operator/tests/rbac/role_binding_test.yaml
 PASS  Test Operator Role       helm/flink-kubernetes-operator/tests/rbac/role_test.yaml
 PASS  Test MutatingWebhookConfiguration        helm/flink-kubernetes-operator/tests/webhook/mutating_webhook_configuration_test.yaml
 PASS  Test Webhook Secret      helm/flink-kubernetes-operator/tests/webhook/secret_test.yaml
 PASS  Test Webhook Service     helm/flink-kubernetes-operator/tests/webhook/service_test.yaml
 PASS  Test ValidatingWebhookConfiguration      helm/flink-kubernetes-operator/tests/webhook/validating_webhook_configuratioin_test.yaml

Charts:      1 passed, 1 total
Test Suites: 14 passed, 14 total
Tests:       52 passed, 52 total
Snapshot:    0 passed, 0 total
Time:        321.49ms

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (no)
• The public API, i.e., is any changes to the CustomResourceDescriptors: (no)
• Core observer or reconciler logic that is regularly executed: (no)

Documentation

• Does this pull request introduce a new feature? (yes)
• If yes, how is the feature documented? (not documented)