feat(website): Metadata documentation for generated fields

[tombch]

This PR does the following:

• Adds definitions for common metadata fields in ‎kubernetes/loculus/templates/_common-metadata.tpl.
• Adds the basic files/config for navigating to and viewing metadata documentation in Loculus (without needing e.g. a Pathoplexus overlay).
• Updates the documentation structure with tabs for input and generated fields, ability to link to a specific field on the page in the URL, and a search bar.

resolves #

Screenshot

PR Checklist

• All necessary documentation has been adapted.
• The implemented feature is covered by appropriate, automated tests.
• Any manual testing that has been done is documented (i.e. what exactly was tested?)

🚀 Preview: https://generated-field-docs.loculus.org