detect/ftp.command: Add sticky buffer

[jlucovsky]

Continuation of #12439

Issue: 7502

Add a sticky buffer for "ftp.command" for matching on FTP command names.

Link to ticket: https://redmine.openinfosecfoundation.org/issues/7502

Describe changes:

• Add a sticky buffer for ftp.command
• Briefly document ftp.command sticky buffer.

Updates

• Documentation: restored missing FTP documentation, removed mention of new keyword from update doc.

Provide values to any of the below to override the defaults.

• To use an LibHTP, Suricata-Verify or Suricata-Update pull request,
  link to the pull request in the respective _BRANCH variable.
• Leave unused overrides blank or remove.

SV_REPO=
SV_BRANCH=OISF/suricata-verify#2245
SU_REPO=
SU_BRANCH=
LIBHTP_REPO=
LIBHTP_BRANCH=

[codecov]

Codecov Report

Attention: Patch coverage is 94.44444% with 2 lines in your changes missing coverage. Please review.

Project coverage is 80.64%. Comparing base (95e8427) to head (e0ed94d).

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #12457      +/-   ##
==========================================
+ Coverage   80.63%   80.64%   +0.01%     
==========================================
  Files         920      921       +1     
  Lines      258704   258740      +36     
==========================================
+ Hits       208595   208665      +70     
+ Misses      50109    50075      -34     

Flag	Coverage Δ
fuzzcorpus	56.83% <50.00%> (+0.02%)	⬆️
livemode	19.43% <50.00%> (+0.03%)	⬆️
pcap	44.31% <50.00%> (-0.03%)	⬇️
suricata-verify	63.23% <94.44%> (-0.03%)	⬇️
unittests	58.52% <50.00%> (-0.01%)	⬇️

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

[victorjulien]

example looks a bit odd. Should use content:"PASS"; I think?

[suricata-qa]

Information: QA ran without warnings.

Pipeline 24330