Improve MongoosePush's logs on 4xx errors

[rslota]

This PR makes it easier to debug errors with MongoosePush / MongooseIM API incompatibility.

[codecov-io]

Codecov Report

Merging #1777 into master will decrease coverage by 0.01%.
The diff coverage is 50%.

@@            Coverage Diff             @@
##           master    #1777      +/-   ##
==========================================
- Coverage   74.47%   74.46%   -0.02%     
==========================================
  Files         290      290              
  Lines       26931    26932       +1     
==========================================
- Hits        20058    20054       -4     
- Misses       6873     6878       +5

Impacted Files	Coverage Δ
src/mod_push_service_mongoosepush.erl	88.57% <50%> (-5.55%)	⬇️
...rc/global_distrib/mod_global_distrib_transport.erl	47.05% <0%> (-5.89%)	⬇️
...bal_distrib/mod_global_distrib_hosts_refresher.erl	84.44% <0%> (-2.23%)	⬇️
src/global_distrib/mod_global_distrib_utils.erl	78.57% <0%> (-1.03%)	⬇️
src/ejabberd_sm.erl	82.87% <0%> (-0.69%)	⬇️
src/mod_muc.erl	72.62% <0%> (-0.28%)	⬇️
src/mod_muc_log.erl	77.94% <0%> (-0.26%)	⬇️
src/mod_roster.erl	78.92% <0%> (-0.25%)	⬇️
src/rdbms/mongoose_rdbms.erl	71.22% <0%> (ø)	⬆️
src/mod_mam_utils.erl	88.09% <0%> (+0.68%)	⬆️
... and 1 more

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