refactor: Rename leaf config to site config

feat: Add argument specs and atomic validation

meta/argument_specs.yml

@@ -0,0 +1,55 @@
+---
+argument_specs:
+  main:
+    short_description: The main entry point for the bind9 role.
+    options:
+      bind9_config:
+        type: list
+        elements: dict
+        description:
+          - A list of configuration dictionaries that are merged to produce the final configuration.
+          - Each element must have a 'name' key (filename).
+      bind9_default_config:
+        type: list
+        elements: dict
+        description: Default configuration.
+      bind9_group_config:
+        type: list
+        elements: dict
+        description: Group-level configuration.
+      bind9_site_config:
+        type: list
+        elements: dict
+        description: Site/Leaf-level configuration.
+      bind9_host_config:
+        type: list
+        elements: dict
+        description: Host-level configuration.
+      bind9_backup_config:
+        type: bool
+        default: true
+        description: Whether to backup configuration files before overwriting.
+      bind9_debug_config:
+        type: bool
+        default: false
+        description: Whether to print the merged configuration during execution.
+      bind9_config_indent:
+        type: int
+        default: 4
+        description: Indentation level for generated configuration files.
+      bind9_packages:
+        type: list
+        elements: str
+        description: List of packages to install.
+      bind9_cfgdir:
+        type: str
+        description: Directory for configuration files.
+      bind9_working_directory:
+        type: str
+        description: Working directory for BIND.
+      bind9_libdir:
+        type: str
+        description: Library directory for BIND.
+      bind9_backup_dir:
+        type: str
+        description: Directory for backups.