Migrate linux_host_engine to engine v2. (flutter/engine#41715)

The artifacts generated by legacy and engine v2 are identical. This PR is moving linux host engine to staging and starts uploading engine v2 artifacts to production.

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

engine/src/flutter/.ci.yaml

@@ -183,6 +183,7 @@ targets:
 
   - name: Linux Host Engine
     recipe: engine/engine
+    bringup: true
     properties:
       gclient_variables: >-
         {"download_emsdk": true}

engine/src/flutter/ci/builders/linux_host_engine.json

@@ -76,7 +76,8 @@
                         "out/host_debug/zip_archives/linux-x64/font-subset.zip",
                         "out/host_debug/zip_archives/flutter_patched_sdk.zip",
                         "out/host_debug/zip_archives/dart-sdk-linux-x64.zip"
-                    ]
+                    ],
+                    "realm": "production"
                 }
             ],
             "drone_dimensions": [
@@ -176,7 +177,8 @@
                     "type": "gcs",
                     "include_paths": [
                         "out/host_release/zip_archives/flutter_patched_sdk_product.zip"
-                    ]
+                    ],
+                    "realm": "production"
                 }
             ],
             "drone_dimensions": [