feat(configuration): support multiple vaults in the configuration file (#6)

When multiple vaults are added to the configuration file, the script will prompt 
you to select one at runtime

src/obsidian_metadata/_config/__init__.py

@@ -1,5 +1,5 @@
 """Config module for obsidian frontmatter."""
 
-from obsidian_metadata._config.config import Config
+from obsidian_metadata._config.config import Config, VaultConfig
 
-__all__ = ["Config"]
+__all__ = ["Config", "VaultConfig"]