chore: document keepAliveInitialDelayMillis option

Author: hjr3

docs/pages/apis/client.mdx

@@ -23,6 +23,7 @@ type Config = {
   lock_timeout?: number, // number of milliseconds a query is allowed to be en lock state before it's cancelled due to lock timeout
   application_name?: string, // The name of the application that created this Client instance
   connectionTimeoutMillis?: number, // number of milliseconds to wait for connection, default is no timeout
+  keepAliveInitialDelayMillis?: number, // set the initial delay before the first keepalive probe is sent on an idle socket
   idle_in_transaction_session_timeout?: number, // number of milliseconds before terminating any session with an open idle transaction, default is no timeout
   client_encoding?: string, // specifies the character set encoding that the database uses for sending data to the client
   fallback_application_name?: string, // provide an application name to use if application_name is not set