feat: add pre-commit check in ci

- add a ci workflow to verify pre-commit passes
- fix pre-commit errors/warnings:
  - missing required_version
  - missing required_providers
  - fixed terraform_deprecated_interpolation
  - removed terraform_unused_declarations

modules/vault_cluster/modules/pki_mount_only/variables.tf

@@ -89,4 +89,4 @@ variable "delta_rebuild_interval" {
   description = "Delta CRL rebuild interval"
   type        = string
   default     = null
-}
+}

modules/vault_cluster/modules/pki_secret_backend/variables.tf

@@ -61,6 +61,12 @@ variable "enable_templating" {
   default     = false
 }
 
+variable "default_issuer_ref" {
+  description = "Reference to the default issuer"
+  type        = string
+  default     = null
+}
+
 variable "default_follows_latest_issuer" {
   description = "Whether the default issuer should follow the latest issuer"
   type        = bool
@@ -101,4 +107,4 @@ variable "delta_rebuild_interval" {
   description = "Delta CRL rebuild interval"
   type        = string
   default     = null
-}
+}