Allow mods to claim user config files and display them in config tab

[robojumper]

Use case: My F1 (incl. WotC version) has a file XComYAF1_NullConfig.ini in the user directory (%USERPROFILE%/Documents/My Games/XCOM2 War of the Chosen/XComGame/Config). This is the file users are supposed to edit (for example for rebinding), and I guarantee that their changes persist through mod updates.

AML, on the other hand, only shows the config files shipped with the mod in its Config folder. Users are not supposed to edit any of them -- they're only there to make my life easier because filling in data is easier within config files.

It would be great if my mod could specify somewhere that XComYAF1_NullConfig.ini is "my" file and AML would show that file by default in the Config tab.

[Xymanek]

Related: #200 (comment)

(both issues are about mods providing some metadata to AML)

[MrNiceUK]

Converse of "hiding" config files would make sense too