[et] Prepare local_engine.json for CI, teach et to understand local b…

…uild names (#51803)

This is steps (2) and (3) of
flutter/flutter#145263.

The next steps after this are to:
1. Fix any issues that come up when running `local_engine.json` in CI.
1. Step (4) of flutter/flutter#145263
1. Fill in some missing builds in `local_engine.json`.

.ci.yaml

@@ -49,6 +49,14 @@ platform_properties:
 # https://chromium.googlesource.com/chromium/src.git/+/HEAD/tools/android/avd/proto
 # You may use those names for the android_virtual_device version.
 targets:
+  - name: Linux local_engine_builds
+    bringup: true
+    enabled_branches:
+      - main
+    recipe: engine_v2/engine_v2
+    properties:
+      config_name: local_engine
+
   - name: Linux linux_android_emulator_tests
     enabled_branches:
       - main