lowercase HTTP headers in mod_bosh for HTTP/2 compliance

[cogentParadigm]

This PR addresses #2210

Proposed changes include:

• make HTTP headers lowercase to avoid HTTP/2 connection errors

[michalwski]

Thanks for the changes. There is a test case in bosh_SUITE https://github.com/esl/MongooseIM/blob/master/big_tests/tests/bosh_SUITE.erl#L230-L238 which compares some headers in case sensitive manner. Could fix the test so that it passes with your changes?

[codecov]

Codecov Report

Merging #2211 into master will decrease coverage by 0.15%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #2211      +/-   ##
==========================================
- Coverage   78.88%   78.73%   -0.16%     
==========================================
  Files         333      333              
  Lines       28682    28699      +17     
==========================================
- Hits        22625    22595      -30     
- Misses       6057     6104      +47

Impacted Files	Coverage Δ
src/mod_bosh.erl	95% <100%> (ø)	⬆️
src/auth/ejabberd_auth_pki.erl	16.66% <0%> (-18.12%)	⬇️
..._distrib/mod_global_distrib_outgoing_conns_sup.erl	73.91% <0%> (-8.7%)	⬇️
src/mam/mod_mam_muc_rdbms_async_pool_writer.erl	63.54% <0%> (-4.17%)	⬇️
src/mam/mod_mam_rdbms_prefs.erl	92.52% <0%> (-3.74%)	⬇️
src/rdbms/mongoose_rdbms.erl	68.87% <0%> (-2.56%)	⬇️
...bal_distrib/mod_global_distrib_hosts_refresher.erl	82.22% <0%> (-2.23%)	⬇️
src/mod_muc_room.erl	76.62% <0%> (-1.06%)	⬇️
src/cassandra/mongoose_cassandra_worker.erl	74.38% <0%> (-0.99%)	⬇️
src/mam/mod_mam_utils.erl	82.78% <0%> (-0.67%)	⬇️
... and 4 more

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[cogentParadigm]

done. Thanks for pointing me in the right direction.

[michalwski]

Thanks for the patch!