fix(effects): dispatch init action once

[timdeschryver]

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?

Closes #2106

What is the new behavior?

See the breaking change section below

Does this PR introduce a breaking change?

[x] Yes
[ ] No

BREAKING CHANGE

Before
When the effect class was registered, the init action would be dispatched.
If the effect was provided in multiple lazy loaded modules, the init action would be dispatched for every module.

After
The init action is only dispatched once
The init action is now dispatched based on the identifier of the effect (via ngrxOnIdentifyEffects)

[ngrxbot]

Preview docs changes for fa218a7 at https://previews.ngrx.io/pr2164-fa218a7/

[ngrxbot]

Preview docs changes for cae8460 at https://previews.ngrx.io/pr2164-cae8460/