MM-56082 Add PreferencesHaveChanged plugin hook (#25659)

* Add interface for PreferencesHaveChanged hook

* Add context to preference-related methods of App

* Implement PreferencesHaveChanged

* Re-add missing "fmt" import

* Update minimum server version for the new hook

* Remove pointers to be consistent with other preference APIs

server/channels/app/export_test.go

@@ -104,7 +104,7 @@ func TestExportUserChannels(t *testing.T) {
 	require.NoError(t, err)
 
 	th.App.UpdateChannelMemberNotifyProps(th.Context, notifyProps, channel.Id, user.Id)
-	exportData, appErr := th.App.buildUserChannelMemberships(user.Id, team.Id, false)
+	exportData, appErr := th.App.buildUserChannelMemberships(th.Context, user.Id, team.Id, false)
 	require.Nil(t, appErr)
 	assert.Equal(t, len(*exportData), 3)
 	for _, data := range *exportData {