feat(docs): Expose tooling for rule developers

[lifeforms]

Motivation

We need more input from new contributors. Currently, we are relying more and more on a lot of internal and external tools to write our rules. Not everybody may know them, while they are so helpful to create better rules.

I think we should have something like a "Great tools for rule writers" page to bring the rule writing practices from the 2000s to the 2020s.

And maybe even end with a full-fledged "rule writing walkthrough" that strings all the tools together to create a sample rule (could be moved to a separate issue if we want to do that).

Proposed solution

At least, we could make a list of useful tools and links to them.

For example:

• CRS-toolchain (would link to our own upcoming documentation page about the new regexp assembler)
• go-ftw (link to our own upcoming documentation)
• https://regex101.com - This is essential
• https://onecompiler.com/mysql - live running MySQL commands (great site btw)
• https://onecompiler.com/mongodb - live running MongoDB commands
• https://sqliteonline.com - live running SQLite commands
• https://onecompiler.com/redis - live running Redis commands
• ...anything else that you love?

At best we could have the list, and also create a 'walkthrough' for creating a rule that goes from:

• a payload
• to one of the online IDEs above to play with payload variances and backend behavior with regards to spacing, comments, etc.
• to thinking of a regexp
• to making and testing it in regex101
• when to modify an existing rule and when to create a new rule (which should be somewhat discouraged unless it's really a new attack technique.)
• then to create a regexp-assemble data file
• generate the rule with crs-toolchain
• testing the rule (link to our own upcoming documentation on go-ftw)

Alternatives

Karel always just does a web search for 'execute postgres online'. But there's a bigger chance that people might give up.

Additional context

N/A

[fzipi]

Shall we move this one to https://github.com/coreruleset/documentation ?

[dune73]

It's a great proposal btw.