pkt-data: add userguide entry, fix typo - v1

[jufajardini]

While working for alert metadata testing for PGSQL, I was looking for more info on pkt-data and realized we didn't have a rules-guide entry for it. The description here is based on what I saw in https://docs.snort.org/rules/options/payload/, considering we mention pkt_data in some sections of our documentation that mention Snort.

Link to redmine ticket: none

Describe changes:

• add pkt_data keyword section to userguide/rules/payload-keywords
• Updated the comment description for the registering function, replacing file_data with pkt_data.
• Fix section title formatting for section about PCRE1 and PCRE2 differences

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 82.80%. Comparing base (3a27cfd) to head (c49e7fb). Report is 11 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #10938      +/-   ##
==========================================
+ Coverage   82.74%   82.80%   +0.06%     
==========================================
  Files         922      922              
  Lines      247861   248217     +356     
==========================================
+ Hits       205081   205536     +455     
+ Misses      42780    42681      -99     

Flag	Coverage Δ
fuzzcorpus	64.15% <100.00%> (+0.16%)	:arrow_up:
suricata-verify	62.42% <100.00%> (+<0.01%)	:arrow_up:
unittests	62.25% <100.00%> (+0.03%)	:arrow_up:

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

[suricata-qa]

WARNING:

field	baseline	test	%
	SURI_TLPR1_stats_chk
.memcap.pressure	57	59	103.51%

Pipeline 20312

[victorjulien]

Are you planning to resubmit soon?

[jufajardini]

Are you planning to resubmit soon?

As I tried to improve on this one, I felt I was lacking some knowledge to write something that made sense. I'll close it for now, to reduce the open PRs noise.