Multitenancy for the Client REST API for MAM and MUC-light

[arcusfelis]

This PR addresses "Multitenancy for the Client REST API for MAM and MUC-light".

Proposed changes include:

• rooms and messages endpoints

• roster not included, because roster does not support MT yet.

• We also log more in rest_helper in tests now (similar to the way we log stanzas).

[codecov]

Codecov Report

Merging #3147 (2d15807) into master (647b6fb) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #3147   +/-   ##
=======================================
  Coverage   79.55%   79.55%           
=======================================
  Files         397      397           
  Lines       32322    32327    +5     
=======================================
+ Hits        25714    25719    +5     
  Misses       6608     6608           

Impacted Files	Coverage Δ
...ngoose_client_api/mongoose_client_api_messages.erl	94.73% <100.00%> (+0.09%)	⬆️
.../mongoose_client_api/mongoose_client_api_rooms.erl	89.70% <100.00%> (+0.15%)	⬆️
src/muc_light/mod_muc_light_commands.erl	91.46% <100.00%> (+1.33%)	⬆️
src/muc_light/mod_muc_light_utils.erl	90.00% <100.00%> (+0.20%)	⬆️
src/elasticsearch/mongoose_elasticsearch.erl	76.92% <0.00%> (-7.70%)	⬇️
src/mam/mod_mam_elasticsearch_arch.erl	86.60% <0.00%> (-1.79%)	⬇️
src/wpool/mongoose_wpool.erl	84.00% <0.00%> (-1.00%)	⬇️
src/ejabberd_c2s.erl	88.99% <0.00%> (-0.30%)	⬇️
src/pubsub/mod_pubsub.erl	71.93% <0.00%> (+0.05%)	⬆️
src/mod_roster.erl	76.85% <0.00%> (+0.23%)	⬆️
... and 2 more

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[chrzaszcz]

Looks good in general, I have a few comments.

[chrzaszcz]

Looks good!