detect/transform: from_base64 transform

[jlucovsky]

Continuation of #10991

This PR provides the from_base64 transform used to match on content decoded with base64 using the mode (default rfc4648).

Link to redmine ticket: 6487

Describe changes:

• New transform: from_base64
• Documentation
• Keyword parser in rust.

Updates:

• Doc -- split extra long line and added ref to transform.

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

To use a pull request use a branch name like pr/N where N is the pull request number.

Alternatively, SV_BRANCH may also be a link to an OISF/suricata-verify pull-request.

SV_BRANCH=https://github.com/OISF/suricata-verify/pull/1670

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 94.11765% with 28 lines in your changes are missing coverage. Please review.

Project coverage is 82.90%. Comparing base (ad4185b) to head (afa6dce). Report is 175 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #11007      +/-   ##
==========================================
- Coverage   82.94%   82.90%   -0.05%     
==========================================
  Files         918      919       +1     
  Lines      248784   249141     +357     
==========================================
+ Hits       206351   206546     +195     
- Misses      42433    42595     +162     

Flag	Coverage Δ
fuzzcorpus	64.17% <9.67%> (-0.12%)	:arrow_down:
suricata-verify	62.12% <72.04%> (-0.54%)	:arrow_down:
unittests	62.37% <87.60%> (+0.09%)	:arrow_up:

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

[suricata-qa]

Information: QA ran without warnings.

Pipeline 20460

[jlucovsky]

Continued in #11299