Implement config subcommand

The synopsis is as follows.

List all top-level config keys:

    $ ruff config
    allowed-confusables
    builtins
    cache-dir
    ... etc.

List all config keys in a specific section:

    $ ruff config mccabe
    max-complexity

Describe a specific config option:

    $ ruff config mccabe.max-complexity
    The maximum McCabe complexity to allow before triggering `C901` errors.

    Default value: 10
    Type: int
    Example usage:
    ```toml
    # Flag errors (`C901`) whenever the complexity level exceeds 5.
    max-complexity = 5
    ```

crates/ruff_cli/src/args.rs

@@ -44,6 +44,8 @@ pub enum Command {
         #[arg(long, value_enum, default_value = "pretty")]
         format: HelpFormat,
     },
+    /// List or describe the available configuration options
+    Config { option: Option<String> },
     /// List all supported upstream linters
     Linter {
         /// Output format