PostgreSQL: initial support (MVP)

[jufajardini]

PostgreSQL: add SSL handshake support
-- applayerpgsql/parser: add parsers for request and response messages
-- applayerpgsql/pgsql: add unittests for parse_response
-- this parser does NOT yet handle what happens after the handshake

Make sure these boxes are signed before submitting your Pull Request -- thank you.

• I have read the contributing guide lines at https://redmine.openinfosecfoundation.org/projects/suricata/wiki/Contributing
• I have signed the Open Information Security Foundation contribution agreement at https://suricata-ids.org/about/contribution-agreement/
• I have updated the user guide (in doc/userguide/) to reflect the changes made (if applicable)

Link to redmine ticket:
https://redmine.openinfosecfoundation.org/issues/4241

Link to previuos PR:
#5832

Describe changes:

• parses ssl response, now, too
• nit: copyright years changed to 2021, since that's the year of implementation for this protocol (is that how it should be?)

Next steps for this mvp:

• recognize an Error message, which the server can also send, after an SSL Encryption request;
• put at least hooks for handling the SSL Startup Handshake (ideally, generate a pcap that shows this, to make things more palpable)
• nit: missing change logger copyright year.

#suricata-verify-pr:
#suricata-verify-repo: https://github.com/jufajardini/suricata-verify/tree/sslhandshake-v0
#suricata-verify-branch:
#suricata-update-pr:
#suricata-update-repo:
#suricata-update-branch:
#libhtp-pr:
#libhtp-repo:
#libhtp-branch:

[codecov]

Codecov Report

Merging #5841 (f567255) into master (62e665c) will decrease coverage by 0.01%.
The diff coverage is 59.75%.

@@            Coverage Diff             @@
##           master    #5841      +/-   ##
==========================================
- Coverage   72.38%   72.36%   -0.02%     
==========================================
  Files         604      606       +2     
  Lines      179369   179451      +82     
==========================================
+ Hits       129837   129862      +25     
- Misses      49532    49589      +57     

Flag	Coverage Δ
suricata-verify	49.13% <58.02%> (-0.02%)	⬇️
unittests	63.05% <14.63%> (-0.03%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

[jufajardini]

Closed with PR #5877