fix(store): add missing StoreConfig and RootStoreConfig exports

[bhalash]

These were missing from modules/store/src/index.ts.

Closes #2007

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/ngrx/platform/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Documentation has been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

@ngrx/store does not export the StoreConfig and RootStoreConfig interfaces from modules/store/src.index.ts, which it should per the NgRx guide.

Closes #2007

What is the new behavior?

@ngrx/store now exports the StoreConfig and RootStoreConfig modules per Using Dependency Injection -> Injecting Feature Config

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[brandonroberts]

@bhalash will you amend the commit and do a force push so CI will pick it up? Thanks

[bhalash]

@brandonroberts Done!

[brandonroberts]

Thanks @bhalash!