There is currently no libgdata with libsoup3 support available, thus
disable build of the Google Tasks support for now. Also add a check
for soupapiversion, to avoid issues in runtime when the option is enabled.

The "reminders-past-days" GSettings option hold how many days old the past reminders
can be. The older reminders are auto-removed once per day. A special value "0" can
be used to not auto-remove the reminders.

Related to https://gitlab.gnome.org/GNOME/evolution-data-server/-/issues/234

This way the providers can define options, which are not shown by default,
but which the user can access easily.

Closes https://gitlab.gnome.org/GNOME/evolution-data-server/-/issues/39

It can happen the GDBus object resets the interface on its own. As the ESource
connects signals on the 'source' interface, it could happen that the authentication
responses were not received due to them being emitted on a new 'source' interface,
which the ESource did not listen to.

It's large enough that it should be better in its own file, than to
share the file with the common utility functions.

Update the SoupSession's auth manager's cache only if the credentials
passed to the function changed. This can help when re-using the ESoupSession
by multiple sources, which all use the same host and credentials.

... and also the includes in the public headers to peer headers.