Requires https://phabricator.wikimedia.org/T344580

In a public (i.e. non-backend) endpoint /wikis/{domain?}, expose data about all wikis (or single one) so it can be consumed by the Discovery feature frontend.

The data returned per wiki should be scrubbed from non-relevant information:

{
  "sitename": <value>
  "domain": <value>
  "isFeatured": <value>
  "description": <value>
  "logo_url": <value>
  "wiki_site_stats": {
    ....
  }
}

The endpoint should allow clients to query for wikis where wikiSiteinfo.pages is greater than 0. The public endpoint needs to be rate limited to prevent abuse. It is read only. It paginates responses.

ACs:

• a list of wikis can be retrieved by calling GET /wikis
• a single wiki can be retreived by calling GET /wikis/<domain>
• Pagination is implememted by passing limit and offset query parameters. A sensible default is used. Responses contain the total number of items.
• Rate limiting is in place
• Wikis can be filtered by is_featured and is_active