SpamAssassain - Header and body test - Add additional information about test syntax

[shoulders]

SYSTEM INFORMATION
OS type and version	Ubuntu Linux 22.04.5
Usermin version	2.102
Virtualmin version	7.20.2 Pro
Theme version	21.20.7
Apache version	2.4.52
Package updates	49 package updates are available

Background

• Related to #957 #959
• I gave this a separate issue because I hope this one can be implemented to help with these pages

The issue

You are able to make and submit rules that do no follow the required convention:

https://spamassassin.apache.org/full/3.1.x/doc/Mail_SpamAssassin_Conf.html

Proposed solution

I would like to add the following text (from the SpamAssassain Docs) to the top of the Header and body tests page to help use the correct syntax.

This will be a useful stop gap because there is no form validation which is what users would expect.

Test names must not start with a number, and must contain only alphanumerics and underscores. It is suggested that lower-case characters not be used, and names have a length of no more than 22 characters, as an informal convention. Dashes are not allowed.

[jcameron]

Instead of that message, couldn't we just block rules with invalid names from being added?

[shoulders]

Would be better + a link maybe.

But I am sure @iliajie said it would be difficult because of UI limitations.

[iliajie]

I think what Jamie meant was that we can implement server-side validation and simply throw an error if a field isn’t set correctly or is left empty... We don’t actually need to do client-side validation.