Kit support

[st-h]

Is your feature request related to a problem? Please describe.
The font awesome website proposes to make use of Kits when getting started: https://fontawesome.com/v6.0/docs/web/setup/quick-start
However, it seems this feature is not supported by this addon.

Describe the solution you'd like
It is possible to specify the kit url at build time and the addon pulls the necessary icons from this url. Please note that a Kit may include customised icons, that are not present in the npm libraries.

Describe alternatives you've considered
I've added custom icons (svg markup) to templates directly instead of making use of this addon.