feat(lib): lazy url config

[ChristopherPHolder]

Description

Allow the user to have a lazy configuration for the svg by allowing the url option to return an observable and reacting to the change.

provideFastSVG({
      url: (name: string) => timer(10000).pipe(map(() => `assets/svg-icons/${name}.svg`)),
}),

These changes do not seem to break the open-closed principle and do not cause breaking changes.

However, this does mean typing for the options a little less strict. As SvgLoadStrategy.load now takes a string | Observable and this is not inferred.

Additionally, this is only really possible because of the new function runInInjectionContext because a real user will most likely use a service and not a simple function that returns an observable.

Closes: #77

Notes
This is a draft, still need to cleanup code

[eneajaho]

It looks good to me!