Add gems remote type for RubyGems (#142)

Ruby builds fetch gems from rubygems.org directly because artifactapi has no RubyGems remote type.

- add `gems` package type proxying `https://rubygems.org`-style sources
- treat `versions`, `names`, `info/*` and `*specs.4.8.gz` as mutable, `gems/*.gem` and `quick/Marshal.4.8/*.gemspec.rz` as immutable
- serve `api/v1/*.json` as `application/json`
- add a gem/bundler usage snippet to the UI and a gems e2e caching case

Requires unkin/artifactapi#148 (HEAD route; RubyGems probes `HEAD /versions`).

Reviewed-on: #142
Co-authored-by: unkin-agent <unkin-agent@unkin.net>
Co-committed-by: unkin-agent <unkin-agent@unkin.net>

ui/src/components/UsageInstructions.tsx

@@ -243,6 +243,16 @@ index = "sparse+${proxy}/"`,
         },
       ];
 
+    case 'gems':
+      return [
+        {
+          title: 'Use this remote as the RubyGems source',
+          language: 'bash',
+          code: `gem sources --clear-all --add ${proxy}/
+bundle config mirror.https://rubygems.org ${proxy}`,
+        },
+      ];
+
     case 'nuget':
       return [
         {

ui/src/pages/Locals.tsx

@@ -18,6 +18,7 @@ const typeColors: Record<string, 'blue' | 'green' | 'yellow' | 'red' | 'default'
   terraform: 'blue',
   goproxy: 'green',
   cargo: 'yellow',
+  gems: 'red',
   nuget: 'blue',
 };
 

ui/src/pages/Remotes.tsx

@@ -18,6 +18,7 @@ const typeColors: Record<string, 'blue' | 'green' | 'yellow' | 'red' | 'default'
   terraform: 'blue',
   goproxy: 'green',
   cargo: 'yellow',
+  gems: 'red',
   nuget: 'blue',
 };