feat(plugin-seo): add german translation

[fsyntax]

Included a German translation file and updated index.ts to import it.

Description

• I have read and understand the CONTRIBUTING.md document in this repository.

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

[paulpopus]

Hey @fsyntax thanks a lot for your contribution here! Could you please open this PR for beta as well so we have these translations in v3? I'll merge both once tests pass

[fsyntax]

Hey @paulpopus! Sure, I'll open the PR for beta as well. Thanks for the response :)