fix(richtext-lexical): link html converter: serialize newTab to target="_blank"

[linobino1]

Issue #5256 re-appeared in Payload v.3.x-beta, this PR fixes it again.

Type of Change:

• Chore (non-breaking change which does not add functionality)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Change to the templates directory (does not affect core functionality)
• Change to the examples directory (does not affect core functionality)
• This change requires a documentation update

Checklist:

• I have added tests that prove my fix is effective or that my feature works
• Existing test suite passes locally with my changes
• I have made corresponding changes to the documentation

[AlessioGr]

Thank you!!