feat: extra headers parameter in client options (#2091)

Closes #1106

Unfortunately, these need to be set at the connection level. I
investigated whether if we let users provide a callback they could use
`AsyncLocalStorage` to access their context. However, it doesn't seem
like NAPI supports this right now. I filed an issue:
https://github.com/napi-rs/napi-rs/issues/2456

python/src/connection.rs

@@ -223,6 +223,7 @@ pub struct PyClientConfig {
     user_agent: String,
     retry_config: Option<PyClientRetryConfig>,
     timeout_config: Option<PyClientTimeoutConfig>,
+    extra_headers: Option<HashMap<String, String>>,
 }
 
 #[derive(FromPyObject)]
@@ -274,6 +275,7 @@ impl From<PyClientConfig> for lancedb::remote::ClientConfig {
             user_agent: value.user_agent,
             retry_config: value.retry_config.map(Into::into).unwrap_or_default(),
             timeout_config: value.timeout_config.map(Into::into).unwrap_or_default(),
+            extra_headers: value.extra_headers.unwrap_or_default(),
         }
     }
 }