fix: allow user to delete unsent messages

[KeeJef]

This is a proxy pull request from the following codeberg branch, https://codeberg.org/gravel/session-desktop/commits/branch/delete-unsent-messages

Messages sent to open groups can fail to send.

However, users are unable to delete unsent open group messages,
as the 'Delete for everyone' option mandates that
open group messages must be deleted from the server
before being deleted locally, and no other delete option is shown.
Furthermore, in open groups, the 'Delete just for me' option
fails to trigger a distinct code path from 'Delete for everyone'.

This commit enables the 'Delete just for me' context menu option
for all outgoing messages with status 'error'.
To direct the user to the appropriate action,
this commit also hides the 'Delete for everyone' option
for the same messages. Lastly, it also implements the missing
'Delete for me' functionality for open group messages.

Relates: #2745

[burtonemily]

Looks good 👌

[Bilb]

closing this in favor of #3061