Schematic for customisable error handling migration

[zakhenry]

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?

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[x] Other... Please describe: Migration schematic to migrate breaking change introduced in effects.

What is the current behavior?

#2295 introduces a breaking change, this PR adds a migration to ease the transition to ngrx@9 for developers.

Closes #

What is the new behavior?

On upgrade to ngrx 9 developers can run the migration to automatically fix the renamed configuration variable

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

This PR is pending the merge of #2295, thus it currently contains those commits.

[ngrxbot]

Preview docs changes for eefe761 at https://previews.ngrx.io/pr2335-eefe761/

[zakhenry]

Rebased on master now that the dependent PR has merged.

[timdeschryver]

I like this approach more in comparison to what we first had 👏

[timdeschryver]

LGTM