Add WebDAV support to storage-cli client and improve test quality

 Enable WebDAV/DAV provider support in StorageCliClient by adding 'dav'
  to STORAGE_CLI_TYPES and mapping legacy 'webdav' provider name to 'dav'.

  Test improvements:
  - Add comprehensive tests for all legacy provider mappings (AzureRM,
    AWS, Google, aliyun, webdav)
  - Add test for native 'dav' storage-cli type
  - Use begin/ensure blocks to prevent tempfile leaks on test failures
  - Add helper methods (write_config_file, stub_config_for_droplets) to
    reduce repetition
  - Stub additional_flags in #run_cli tests for stability
  - Fix test descriptions for accuracy

Author: kathap

lib/cloud_controller/blobstore/storage_cli/storage_cli_client.rb

@@ -17,16 +17,16 @@ class StorageCliClient < BaseClient
         'resource_pool' => :storage_cli_config_file_resource_pool
       }.freeze
 
-      # Native storage-cli type names supported by CC (dav intentionally excluded for now)
-      STORAGE_CLI_TYPES = %w[azurebs alioss s3 gcs].freeze
+      # Native storage-cli type names supported by CC
+      STORAGE_CLI_TYPES = %w[azurebs alioss s3 gcs dav].freeze
 
       # DEPRECATED: Legacy fog provider names (remove after migration window)
       LEGACY_PROVIDER_TO_STORAGE_CLI_TYPE = {
         'AzureRM' => 'azurebs',
         'aliyun' => 'alioss',
         'AWS' => 's3',
-        'Google' => 'gcs'
-        # 'webdav' => 'dav', # intentionally not enabled yet
+        'Google' => 'gcs',
+        'webdav' => 'dav'
       }.freeze
 
       def initialize(directory_key:, resource_type:, root_dir:, min_size: nil, max_size: nil)
@@ -39,10 +39,6 @@ def initialize(directory_key:, resource_type:, root_dir:, min_size: nil, max_siz
         provider = cfg['provider']&.to_s
         raise BlobstoreError.new("No provider specified in config file: #{File.basename(config_file_path)}") if provider.nil? || provider.empty?
 
-        # Explicitly block unfinished webdav storage-cli support to avoid confusion and wasted effort on debugging
-        # unsupported providers. Remove this check when webdav support is added.
-        raise "provider '#{provider}' is not supported yet" if %w[webdav dav].include?(provider)
-
         @storage_type =
           if STORAGE_CLI_TYPES.include?(provider)
             provider