Permit use of modulo operator within HTL conditionals

The restriction to only allow logical and comparative operators in HTL means modulus operations can't be performed.

```

...

As well as using a constant ("5" in the example above) it should also be possible to use a HTL variable declared before the list or the result of a call into a Java model method, provided the value can be cast to an Integer.

While this does allow very limited business logic into the HTL layer, it's hard to see any other way of implementing a requirement within the list feature. This has been discussed in the past by other users here: https://experienceleaguecommunities.adobe.com/t5/adobe-experience-manager/can-we-use-modulo-in-sightly/td-p/260156

Start by reading the HTL specification's existing operator restrictions and the linked discussion about modulo support. Define how the modulo operator works with constants, previously declared HTL variables, and Java model results castable to Integer; done means the specification states these accepted cases and their constraints.

Written by the indexing model from the issue text.