feat: add local_ssd_encryption_mode

[DrFaust92]

• some README formatting

[apeabody]

/gcbrun

[apeabody]

From the LINT:

1 issue(s) found:

Warning: [Fixable] variable "local_ssd_encryption_mode" is declared but not used (terraform_unused_declarations)

  on variables.tf line 438:
 438: variable "local_ssd_encryption_mode" {

Reference: https://github.com/terraform-linters/tflint-ruleset-terraform/blob/v0.10.0/docs/rules/terraform_unused_declarations.md

tflint failed ./modules/private-cluster 
Working in ./modules/private-cluster-update-variant using /root/tflint/.tflint.module.hcl...
1 issue(s) found:

Warning: [Fixable] variable "local_ssd_encryption_mode" is declared but not used (terraform_unused_declarations)

  on variables.tf line 438:
 438: variable "local_ssd_encryption_mode" {

Reference: https://github.com/terraform-linters/tflint-ruleset-terraform/blob/v0.10.0/docs/rules/terraform_unused_declarations.md

tflint failed ./modules/private-cluster-update-variant 

[apeabody]

/gcbrun

[apeabody]

From the test:

        	Error Trace:	/builder/home/go/pkg/mod/github.com/gruntwork-io/[email protected]/modules/terraform/apply.go:34
        	            				/builder/home/go/pkg/mod/github.com/!google!cloud!platform/cloud-foundation-toolkit/infra/[email protected]/pkg/tft/terraform.go:571
        	            				/builder/home/go/pkg/mod/github.com/!google!cloud!platform/cloud-foundation-toolkit/infra/[email protected]/pkg/tft/terraform.go:630
        	            				/builder/home/go/pkg/mod/github.com/!google!cloud!platform/cloud-foundation-toolkit/infra/[email protected]/pkg/tft/terraform.go:669
        	            				/builder/home/go/pkg/mod/github.com/!google!cloud!platform/cloud-foundation-toolkit/infra/[email protected]/pkg/utils/stages.go:31
        	            				/builder/home/go/pkg/mod/github.com/!google!cloud!platform/cloud-foundation-toolkit/infra/[email protected]/pkg/tft/terraform.go:669
        	Error:      	Received unexpected error:
        	            	FatalError{Underlying: error while running command: exit status 1; 
        	            	Error: expected node_pool.0.node_config.0.local_ssd_encryption_mode to be one of ["STANDARD_ENCRYPTION" "EPHEMERAL_KEY_ENCRYPTION"], got 
        	            	
        	            	  with module.example.module.gke.google_container_cluster.primary,
        	            	  on ../../../cluster.tf line 502, in resource "google_container_cluster" "primary":
        	            	 502:       local_ssd_encryption_mode = lookup(var.node_pools[0], "local_ssd_encryption_mode", "")
        	            	}
        	Test:       	TestDeployService