feat: notification processor improvements

Notification processor functions are now renamed to `preProcess` and `postProcess`.
Additionally, processor name is now required to be returned by `getName`.
A new processor functionality `processOptions` was added to process options before sending the notification.

Signed-off-by: Heikki Hellgren <heikki.hellgren@op.fi>

plugins/notifications-common/api-report.md

@@ -12,7 +12,7 @@ export type NewNotificationSignal = {
 // @public (undocumented)
 type Notification_2 = {
   id: string;
-  user: string;
+  user: string | null;
   created: Date;
   saved?: Date;
   read?: Date;

plugins/notifications-common/src/types.ts

@@ -33,7 +33,7 @@ export type NotificationPayload = {
 /** @public */
 export type Notification = {
   id: string;
-  user: string;
+  user: string | null;
   created: Date;
   saved?: Date;
   read?: Date;