feat: complete Kra admin backend migration

internal/conf/conf.proto

@@ -17,13 +17,7 @@ message Server {
     string addr = 2;
     google.protobuf.Duration timeout = 3;
   }
-  message GRPC {
-    string network = 1;
-    string addr = 2;
-    google.protobuf.Duration timeout = 3;
-  }
   HTTP http = 1;
-  GRPC grpc = 2;
 }
 
 message Data {
@@ -58,6 +52,7 @@ message AdminBackend {
   Storage storage = 6;
   // ConfigPath is populated by the entrypoint and is not required in YAML.
   string config_path = 7;
+  Media media = 8;
 
   message JWT {
     string signing_key = 1;
@@ -89,6 +84,10 @@ message AdminBackend {
     bool is_login_auth = 8;
   }
 
+  message Media {
+    int32 session_ttl = 1;
+  }
+
   message Storage {
     string type = 1;
     Qiniu qiniu = 2;