chore(docs): use new 'default_region' provider attribute (#793)

instead of deprecated 'region' attribute

docs/guides/aws_provider_s3_stackit.md

@@ -15,7 +15,7 @@ This guide outlines the process of utilizing the [AWS Terraform Provider](https:
 
       ```hcl
       provider "stackit" {
-         region = "eu01"
+         default_region = "eu01"
       }
       ```
 

docs/guides/kubernetes_provider_ske.md

@@ -15,7 +15,7 @@ This guide outlines the process of utilizing the [HashiCorp Kubernetes provider]
 
     ```hcl
     provider "stackit" {
-      region = "eu01"
+      default_region = "eu01"
     }
     ```
 

docs/guides/opting_into_beta_resources.md

@@ -19,7 +19,7 @@ Set the `enable_beta_resources` option in the provider configuration. This is a
 
 ```hcl
 provider "stackit" {
-  region                = "eu01"
+  default_region        = "eu01"
   enable_beta_resources = true
 }
 ```

docs/guides/ske_kube_state_metric_alerts.md

@@ -13,7 +13,7 @@ This guide explains how to configure the STACKIT Observability product to send a
 
    ```hcl
    provider "stackit" {
-     region = "eu01"
+     default_region = "eu01"
    }
 
    provider "kubernetes" {

docs/guides/vault_secrets_manager.md

@@ -13,7 +13,7 @@ This guide outlines the process of utilizing the [HashiCorp Vault provider](http
 
     ```hcl
     provider "stackit" {
-      region = "eu01"
+      default_region = "eu01"
     }
     ```
 

docs/index.md

@@ -6,27 +6,27 @@ The STACKIT Terraform provider is the official Terraform provider to integrate a
 
 ```terraform
 provider "stackit" {
-  region = "eu01"
+  default_region = "eu01"
 }
 
 # Authentication
 
 # Token flow
 provider "stackit" {
-  region                = "eu01"
+  default_region        = "eu01"
   service_account_token = var.service_account_token
 }
 
 # Key flow
 provider "stackit" {
-  region              = "eu01"
+  default_region      = "eu01"
   service_account_key = var.service_account_key
   private_key         = var.private_key
 }
 
 # Key flow (using path)
 provider "stackit" {
-  region                   = "eu01"
+  default_region           = "eu01"
   service_account_key_path = var.service_account_key_path
   private_key_path         = var.private_key_path
 }