Function execute_interceptor 

pub async fn execute_interceptor(
    plugin: &CrdPlugin,
    crd_kind: &str,
    headers: &HashMap<String, String>,
    body: &str,
    db_path: Option<&Path>,
) -> Result<()>

Execute an interceptor plugin (e.g. custom signature verification).

The plugin receives context via environment variables:

• PLUGIN_NAME, PLUGIN_TYPE, CRD_KIND: plugin identity
• WEBHOOK_BODY: raw request body
• WEBHOOK_HEADER_<NAME>: one variable per HTTP header (uppercased, hyphens→underscores)

Returns Ok(()) if the plugin exits 0 (accept), or Err if non-zero (reject).