Enable validation of fetchers

Related to #72 (closed)

• As an economist validating a fetcher
• I want to view data downloaded, converted and indexed in the "next" UI
• in order to validate a fetcher

Acceptance criteria

Search results home page

• Provider properties {name, long_name} MUST be displayed in the search results cards
• Datasets properties {code, name} MUST be displayed in search results cards
• Provider names MUST be links to "provider" page

Provider page

• A new "provider" page MUST be added under the URL path /<provider_slug>
• All the provider properties MUST be displayed
• The categories tree MUST be displayed
• When clicking on a node of the categories tree, the node MUST collapse or expand

Dataset page

• Dimensions MUST be displayed
• Attributes about series MUST be displayed
• Attributes about measures MUST appear in downloadable TSV files
• Series of a dataset MUST appear
• Series MUST be paginated (50 per page)
• Series properties {key, name} MUST be displayed

Resources

• The categories tree does not need to be searchable/filtered, just use Ctrl-F of the browser for now.
• Suggestion: use the <details> and <summary> HTML elements.