fix(component): add entry point for schematic

[Jefiozie]

Added the entry point for the schematic so that the error is resolved.

PR Checklist

Please check if your PR fulfills the following requirements:

• [ X 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?

When running ng add @ngrx/component you will see an error

Closes #2683

What is the new behavior?

Because we've added the entrypoint we should not see the error any more.

Does this PR introduce a breaking change?

[ ] Yes
[x ] No

Other information

[ngrxbot]

Preview docs changes for a3c138b at https://previews.ngrx.io/pr2688-a3c138b4/

[timdeschryver]

Thanks @Jefiozie !