feat(effects): remove @Effect decorator

[timdeschryver]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https:/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?

[ ] Bugfix
[x] 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 #3617

What is the new behavior?

Does this PR introduce a breaking change?

[x] Yes
[ ] No

BREAKING CHANGE:

The @effect decorator is removed

BEFORE:
Defining an effect is done with @effect

@effect()

data$ = this.actions$.pipe();

AFTER:

Defining an effect is done with createEffect

data$ = createEffect(() => this.actions$.pipe());

Other information

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[brandonroberts]

✌🏿🎉

[markostanimirovic]

🎉