Allow Admins to view, edit and delete past and current announcements

[Tinitto]

Is your feature request related to a problem? Please describe.
Currently it seems impossible for an admin to edit an announcement they have made, let alone delete them.
In fact if that admin clears that announcement, the only way to find it again is to go to pocketbase's '/_/' dashboard.

Describe the solution you'd like
In the 'Broadcast Announcement' tab of the 'Admin panel', let's add a scroll-list of all announcements
Each with an option to expand (or read more?), an option to edit, and an option to delete

Describe alternatives you've considered
N/A

Additional context