Multitenancy for ejabberd users

[NelsonVides]

This erases ejabberd_users and creates a new module called mongoose_users that implements pretty much the same cache idea, but creates a table per host_type, and implements the remove_domain hook.

It also chooses to extract the host_type from the accumulator in some places where we can be sure we do have a host_type, like, when run inside user_send_packet, filter_local_packet, or iq handlers.

[codecov]

Codecov Report

Merging #3135 (c51ebed) into master (e55fa8e) will increase coverage by 0.02%.
The diff coverage is 94.73%.

@@            Coverage Diff             @@
##           master    #3135      +/-   ##
==========================================
+ Coverage   79.46%   79.49%   +0.02%     
==========================================
  Files         395      395              
  Lines       32172    32170       -2     
==========================================
+ Hits        25565    25572       +7     
+ Misses       6607     6598       -9     

Impacted Files	Coverage Δ
src/mongoose_hooks.erl	92.30% <ø> (ø)
src/mongoose_users.erl	93.02% <93.02%> (ø)
src/auth/ejabberd_auth.erl	83.87% <100.00%> (ø)
src/ejabberd_app.erl	93.75% <100.00%> (ø)
...t_pusher/mod_event_pusher_push_plugin_defaults.erl	93.10% <100.00%> (+0.12%)	⬆️
src/inbox/mod_inbox.erl	90.50% <100.00%> (+0.09%)	⬆️
src/mam/mod_mam.erl	89.15% <100.00%> (+0.05%)	⬆️
src/muc_light/mod_muc_light.erl	84.54% <100.00%> (ø)
src/pubsub/node_hometree.erl	77.77% <0.00%> (-5.56%)	⬇️
...bal_distrib/mod_global_distrib_hosts_refresher.erl	71.69% <0.00%> (-1.89%)	⬇️
... and 9 more

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[DenysGonchar]

looks fine for now, mongoose_users must be reimplemented with the proper caching solution once we pick one.