Milo: Store console defs as their own entities

milo/api/config/project.proto

 // Copyright (c) 2016 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 syntax = "proto3";
 
 package config;
 
 // Project is a project definition for Milo.
 message Project {
@@ skipping 10 matching lines @@
   // console reachable from /console/<Project>/<ID>.
   string ID = 1;
 
   // Name is the longform name of the waterfall, and will be used to be
   // displayed in the title.
   string Name = 2;
 
   // RepoURL is the URL of the git repository to display as the rows of the console.
   string RepoURL = 3;
 
-  // Branch is the branch to pull commits from when displaying the console.
-  string Branch = 4;
+  // Ref is the ref to pull commits from when displaying the console.
+  // Eg. refs/heads/master
+  string Ref = 4;
 
   // ManifestName is the name of the manifest the waterfall looks at.
   // By convention, Manifest Names can be:
   // * UNPATCHED - For non patched builds, such as continuous builds
   // * PATCHED - For patched builds, such as those on try jobs
   string ManifestName = 5;
 
   // Builders is a list of builder configurations to display as the columns of the console.
   repeated Builder Builders = 6;
 }
 
 // A builder is a reference to a Milo builder.
 message Builder {
   // Name is the identifier to find the builder, which includes the module.
   // Buildbot builds would be like "buildbot/chromium.linux/Linux Tests"
   // Buildbucket builds would be like "buildbucket/luci.chromium.try/linux_chromium_rel_ng"
   string Name = 1;
 
   // Category describes the hierarchy of the builder on the header of the
   // console as a "|" delimited list.  Neighboring builders with common ancestors
   // will be have their headers merged.
   string Category = 2;
 
   // ShortName is the 1-3 character abbreviation of the builder.
   string ShortName = 3;
 }