Make metadata docs generally available

[chaoran-chen]

#3477 added a MetadataTable.astro component to show a table with metadata description information but it is not used in the Loculus code but only in the overlay version for Pathoplexus. This feature would be also useful for other Loculus instances and we should generalize it.

Acceptance criteria

• The maintainer can decide in the config on a per-organism level whether a metadata docs. should be available.
• If activated, there should be a link/button on the submit page to open the metadata table.
• The metadata table could be in a modal or in a separate page.