Lists, campaigns, and subscribers tables now support server-side
sorting from the UI. This significantly changes the internal
queries from prepared to string interpolated to support dynamic
sort params.
A new toggle switch in Settings -> Privacy, which is off by
default, allows campaign views (pixel) and link clicks to function
without registering the subscriber ID against view and click
events, anonymising tracking. When off, the subscriber UUIDs in
view and link tracking URLs are removed, anonymising subscriber
information from HTTP logs as well.
This is a major feature that builds upon the `Messenger` interface
that has been in listmonk since its inception (with SMTP as the only
messenger). This commit introduces a new Messenger implementation, an
HTTP "postback", that can post campaign messages as a standard JSON
payload to arbitrary HTTP servers. These servers can in turn push them
to FCM, SMS, or any or any such upstream, enabling listmonk to be a
generic campaign messenger for any type of communication, not just
e-mails.
Postback HTTP endpoints can be defined in settings and they can be
selected on campaigns.
