Default applied search filters for the browse page

[chaoran-chen]

As a maintainer, I want to be able to configure default filters for the search page, so users will see a more relevant search result by default.

Example: show only unrestricted sequences by default, or show only non-flagged sequences (#813) by default.

Acceptance criteria

In the config, its possible to specify search defaults like so (per organism):

searchDefaults:
  <fieldName>: <defaultValue>

When I click on a virus on the landing page, I get to the search page with the defaults already selected.