Allow Generic for featureName for StoreModule.forFeature()

[ZackDeRose]

Describe any alternatives/workarounds you're currently using

Had a task to recently lock down the accepted ngrx feature names to a specific set of names.

To accomplish, we created a typed shim for the StoreModule that overrode the forFeature() method to give a proper type to the featureName param.

Adding another generic to this method (that defaults to any string) should solve this, without causing breaking changes.

Other information:

Discussed this with @brandonroberts, who asked me to open this issue!

If accepted, I would be willing to submit a PR for this feature

[x] Yes (Assistance is provided if you need help submitting a pull request)
[ ] No

[brandonroberts]

Will you add some sample code of what you see the changes enabling?