fix: add optional decorator for property based injection

[jmcdo29]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• 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?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior?

After moving the AuthModuleOptions to a property so that the AuthGuard() could be better extended, Nest started throwing errors about not being able to find the AuthModuleOptions. This is because ti is no longer optional.

Issue Number: #823

What is the new behavior?

Back to the behavior in 8.0.0 with the property being optional, but it's also still a property

Does this PR introduce a breaking change?

• Yes
• No

Other information

I've added in some tests to show it's working without having to use register, I want to add more for a nested set up and show it's fully working, but I don't want to delay this fix from rolling out.

Closes #823

[jmcdo29]

This was a bug introduced, not a (intentional) breaking change. This fixes that bug, and makes the feature work as intended. Though I do believe it should have been a minor bump, not a patch as it does allow for new features to work

[micalevisk]