Add schema validation for collection files #369

This commit improves collection file editing and error detection
directly in the IDE. It adds YAML schema, IDE configuration and
automatic tests to validate it.

- Introduce a YAML schema for collection file.
- Use `yaml-language-server` for enhanced YAML support in VSCode.
- Add telemetry disabling in `configure_vscode.py` to respect user
  privacy.
- Add automated checks to validate YAML file structure against the
  schema.
- Remove unused properties and do not allow them in compiler.

src/application/collections/macos.yaml

@@ -1,4 +1,8 @@
+# yaml-language-server: $schema=./.schema.yaml
+# ↑ Adds a schema support in VS Code for auto-completion and validation.
+
 # Structure is documented in "docs/collection-files.md"
+
 os: macos
 scripting:
     language: shellscript