fix: make the success notice temporary

When the plugin is activated, I print a message to inform users about
settings. However, even if an user dismissed it, the notice is printed
on each page.
By using the transient API with the activation hook, the notice is now
only printed after activation.

includes/class-wp-graphql-gravatar.php

@@ -77,7 +77,11 @@ public function check_plugin_dependencies() {
 	 * @since 1.1.0
 	 */
 	public function print_plugin_activation_success() {
-		include_once 'partials/activation/wp-graphql-gravatar-success.php';
+		if ( get_transient( 'wp-graphql-gravatar-admin-notice' ) ) {
+			include_once 'partials/activation/wp-graphql-gravatar-success.php';
+
+			delete_transient( 'wp-graphql-gravatar-admin-notice' );
+		}
 	}
 
 	/**
@@ -175,6 +179,15 @@ public function add_gravatar_url_field() {
 		);
 	}
 
+	/**
+	 * Set a transient to display a temporary notice on activation.
+	 *
+	 * This function is fired during plugin activation.
+	 */
+	public static function activate() {
+		set_transient( 'wp-graphql-gravatar-admin-notice', true, 5 );
+	}
+
 	/**
 	 * Execute the plugin.
 	 *

wp-graphql-gravatar.php

@@ -37,6 +37,16 @@
  */
 define( 'WP_GRAPHQL_GRAVATAR_VERSION', '1.1.0' );
 
+/**
+ * The code that runs during plugin activation.
+ */
+function activate_wp_graphql_gravatar() {
+	require_once plugin_dir_path( __FILE__ ) . 'includes/class-wp-graphql-gravatar.php';
+	WP_GraphQL_Gravatar::activate();
+}
+
+register_activation_hook( __FILE__, 'WP_GraphQL_Gravatar\activate_wp_graphql_gravatar' );
+
 /**
  * Initialize the plugin.
  *