fix(preload-langs): 🐛 provide in root injector

[Owain94]

PR Checklist

Please check if your PR fulfills the following requirements:

• [ ] The commit message follows our guidelines: https://github.com/ngneat/transloco/blob/master/CONTRIBUTING.md#commit
• [ ] Tests for the changes have been added (for bug fixes / features)
• [ ] Docs have 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?

Using the module causes the following error:

nullinjectorerror: No provider for TranslocoPreloadLangsService!

Issue Number: #726

What is the new behavior?

Does this PR introduce a breaking change?

• [ ] Yes
• [X] No

Other information

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[jhpettit]

@NetanelBasal could this be merged anytime soon? Severely missing being able to preload.