[MERGE][IMP] mail: improve propagation of model through activity type configuration

Activity types can be either generic, either related to a given model.
This task aims at improving the model propagation through several commits

 * prefill model when configuring application activity types;
 * limit previous / next activity types to generic or same model;
 * propagate model when creating new activity types through recommended
   activity m2m;

See sub commits for more details.

This merge is linked to task ID 1844644 and closes PR #25843.

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