Multi tenancy hooks

[DenysGonchar]

this PR reworks ejabberd_hooks in the following way:

• hooks are running either globally or for a host type, not domain name, so they must be registered globally or for a host type as well.
• hooks execution is fully wrapped in mongoose_hooks module.
• when hook handler expect some exact constant initial Acc value, such value is hardcoded mongoose_hooks module. It should not be possible to run the hook with another initial acc value.
• mongoose_acc:t() type is extended with host_type field, this allows to reduce the number of calls to mongoose_domain_api:get_host_type/1 function.
• ejabberd_c2s modules is now running hooks for a host_type, note that only hooks execution is updated. if some hook was expecting a domain name as one of the parameters, it still receives a domain name. we may need to change it in the future, but it requires updates of the hook handlers (which are mostly in the MIM modules).
• remove_domain hook handler implementation for ejaberd_auth

Another big generic module that triggers hooks is ejabberd_sm (13 calls to mongoose_hook). But it should be reworked in a separate PR, and probably after switching back to the master branch.

[codecov]

Codecov Report

Merging #3089 (f65aadf) into multi-tenancy-phase-1 (f991ee2) will increase coverage by 0.64%.
The diff coverage is 89.13%.

@@                    Coverage Diff                    @@
##           multi-tenancy-phase-1    #3089      +/-   ##
=========================================================
+ Coverage                  78.09%   78.74%   +0.64%     
=========================================================
  Files                        374      387      +13     
  Lines                      31219    31691     +472     
=========================================================
+ Hits                       24382    24954     +572     
+ Misses                      6837     6737     -100     

Impacted Files	Coverage Δ
src/admin_extra/service_admin_extra.erl	100.00% <ø> (ø)
src/ejabberd_gen_sm.erl	90.90% <ø> (ø)
src/ejabberd_s2s_in.erl	77.35% <ø> (ø)
src/ejabberd_users.erl	81.63% <ø> (ø)
src/metrics/mongoose_metrics_mam_hooks.erl	86.66% <ø> (ø)
src/mod_stream_management.erl	85.10% <ø> (ø)
src/mongoose_hooks.erl	91.48% <ø> (-0.76%)	⬇️
src/offline/mod_offline_mnesia.erl	51.47% <0.00%> (ø)
src/pubsub/pubsub_form_utils.erl	56.60% <0.00%> (+1.04%)	⬆️
src/rdbms/rdbms_queries_mssql.erl	100.00% <ø> (ø)
... and 146 more

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[chrzaszcz]

I appreciate the huge amount of good work, especially putting the defaults in mongoose_hooks. I have a few comments:

• Are you planning to use mongoose_acc:get_host_type inside the hooks to get rid of the host_type argument for each of them? For me it looks like a natural follow-up.
• Please revise the line breaks in mongoose_hooks to break the comments so that expressions like a server, the client, should be, client jid etc remain in one line. I think it's good practice to do so.

[DenysGonchar]

* Are you planning to use `mongoose_acc:get_host_type` inside the hooks to get rid of the `host_type` argument for each of them? For me it looks like a natural follow-up.

The idea was to reduce calls to mongoose_acc:get_host_type/1 as much as possible. Ideally it should be limited to just one call per incoming message (to identify receiver's host_type, if required), we don't want it to become a bottleneck.

[arcusfelis]

We could always ask for acc argument, that would have host_type field.
and if hook handlers need host_type - they could extract it from the acc.
And if handlers need a domain, they already have server in the acc.

But it's more lines of code to change :D

And after that we could pass Acc everywhere, even into the backend functions.

[chrzaszcz]

One minor comment, please tell me whether you are correcting it or if I should merge.

[chrzaszcz]

Minor: missing commas before Acc1, this happens a few times below.