Add local cargo registry type

- serve sparse index and config.json for local cargo repos from a cargo_index table
- add Web API publish, yank and unyank under the local repo api root
- drop index lines when the crate file is deleted

ui/src/components/UsageInstructions.tsx

@@ -229,6 +229,25 @@ go mod download`,
       ];
 
     case 'cargo':
+      if (isLocal) {
+        return [
+          {
+            title: 'Add the private registry (real sparse registry)',
+            language: 'toml',
+            code: `# $CARGO_HOME/config.toml
+[registries.${name}]
+index = "sparse+${url}/api/v1/local/${name}/"`,
+            note: 'cargo requires a token for publish/yank: set CARGO_REGISTRIES_' + name.toUpperCase().replace(/-/g, '_') + '_TOKEN to any value.',
+          },
+          {
+            title: 'Publish, depend on and yank crates',
+            language: 'bash',
+            code: `cargo publish --registry ${name}
+cargo add <crate> --registry ${name}
+cargo yank --version <version> --registry ${name}`,
+          },
+        ];
+      }
       return [
         {
           title: 'Point crates.io at this sparse registry',