docs: add validation rules

[kapersoft]

Using the magic of the Google Gemini CLI code generator, I have created documentation for the validation rules in located in the Tempest\Validation\Rules-namespace. Each rule document has the following sections:

• Overview - contains one or two sentences about the rule
• Parameters - list of rule parameters (optional)
• Example(s) - One or more examples
• See also - Links to similar rules (optional)

I have placed the rules in a new section called Validation Rules, the first article contains an overview with some generic information. Next section contains links to the the rules organized per category.

Open questions:

• Do you want other kind of examples or sections added to the rule documents?
• Do you want to keep the rules in this location?

Please let me know if you have any questions!

Fixes: tempestphp/tempest-framework#1034

[innocenzi]

I personally don't like that it takes an entire sidebar section.

I am also not sure we want to manually update the docs every time something changes—we discussed internally that we want autogenerated docs, for the string/array utils as well

Maybe we can have these docs pages but hide them from the sidebar though, in the meantime

[brendt]

I appreciate the effort! I don't think this is the way to go though because of the updates Enzo mentioned, but also because we're not 100% sure the generated text is correct without manually reviewing it. If we need to do that, we might as well generate the documentation from our documented code — which we already reviewed.