[WIP] docs: adds documentation to operators.

[jcchavezs]

This PR starts adding the documentation to operators. Plays in tandem with corazawaf/coraza.io#304.

do not merge yet.

[codecov]

Codecov Report

Attention: Patch coverage is 86.66667% with 2 lines in your changes missing coverage. Please review.

Project coverage is 81.99%. Comparing base (681afa9) to head (4bffe24).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/operators/begins_with.go	50.00%	1 Missing ⚠️
internal/seclang/directives.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1340   +/-   ##
=======================================
  Coverage   81.99%   81.99%           
=======================================
  Files         170      170           
  Lines        9803     9803           
=======================================
  Hits         8038     8038           
  Misses       1518     1518           
  Partials      247      247           

Flag	Coverage Δ
coraza.rule.case_sensitive_args_keys	81.95% <86.66%> (ø)
coraza.rule.multiphase_valuation	81.99% <86.66%> (ø)
coraza.rule.no_regex_multiline	81.93% <86.66%> (ø)
default	81.99% <86.66%> (ø)
examples+	16.50% <46.66%> (ø)
examples+coraza.rule.case_sensitive_args_keys	81.95% <86.66%> (ø)
examples+coraza.rule.multiphase_valuation	81.83% <86.66%> (ø)
examples+coraza.rule.no_regex_multiline	81.85% <86.66%> (ø)
examples+memoize_builders	81.95% <86.66%> (ø)
examples+no_fs_access	81.28% <86.66%> (ø)
ftw	81.99% <86.66%> (ø)
memoize_builders	82.08% <86.66%> (ø)
no_fs_access	81.44% <86.66%> (ø)
tinygo	81.96% <86.66%> (ø)

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