core: add avatar provider API

packages/migrate-vijos/package.json

@@ -1,6 +1,6 @@
 {
     "name": "@hydrooj/migrate-vijos",
-    "version": "1.4.1",
+    "version": "1.4.2",
     "main": "package.json",
     "repository": "git@github.com:hydro-dev/Hydro.git",
     "author": "undefined <i@undefined.moe>",

packages/migrate-vijos/script.ts

@@ -23,7 +23,7 @@ const tasks = {
         hash: doc.hash.split('|')[1],
         hashType: doc.hash.split('|')[0] === 'vj4' ? 'hydro' : doc.hash.split('|')[0],
         priv: doc.priv,
-        gravatar: doc.gravatar,
+        avatar: `gravatar:${doc.gravatar}`,
         mail: doc.mail,
         mailLower: doc.mail_lower,
         regat: doc.regat,
@@ -256,7 +256,10 @@ const tasks = {
                 return res;
             },
         },
-        gravatar: 'gravatar',
+        gravatar: {
+            field: 'avatar',
+            processer: (gravatar) => `gavatar:${gravatar}`,
+        },
         bulletin: 'bulletin',
     },
     'fs.files': async (doc) => doc,