Add support for "Groups" tag in Info.xml

[NeilSeligmann]

This PR aims to add support for the Groups tag found in the Info.xml.

The Groups tag, while widely used in many mods, is not in the current version of the schema definition (that I could find).
However, as so many mods use it I found it useful to implement it.

<fomod xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="https://bellcubedev.github.io/site-testing/assets/site/misc/Info.xsd">
    <Name>The BANANA Mod</Name>
    <Author>BellCube</Author>
    <Id>1</Id>
    <Website>https://example.com</Website>
    <Version>1.0.0</Version>
    <Groups>
        <element>category 1</element>
        <element>testGroup2</element>
    </Groups> 
</fomod>

[BellCubeDev]

The main concern with Info.xml in this library is to describe what existing mod managers already implement since there is no official schema. The definitions in the library were derived directly from a trip through the source code for both Vortex and MO2. If you know of a mod manager that uses this the Groups field, I'm completely open to merging this PR in!

I was working on a schema for inclusion in XML files way back in my first iteration of the Fomod Builder. Can't recall why I didn't go with a modified version of it for https://fomod.bellcube.dev/schemas/Info.xsd. That old version: https://github.com/BellCubeDev/site-testing/blob/main/site/src/_includes/Info.xsd

[BellCubeDev]

It may be worth investigating how existing tooling and mod managers handle multi-child elements in Info.xml. I have little knowledge on the subject personally, though the Fomod Creation Tool may be a good place to look if memory serves. I suspect we'll end up creating a class for more complex representations sometime down the line, even if just to handle the element name.