Run the flutter/plugins tests on presubmit, make it part of the tree status (#71502)

dev/prod_builders.json

@@ -162,6 +162,12 @@
         "task_name":"linux_web_smoke_test",
         "flaky":false
       },
+      {
+         "name":"Linux flutter_plugins",
+         "repo":"flutter",
+         "task_name":"flutter_plugins",
+         "flaky":false
+      },
       {
          "name": "Mac build_aar_module_test",
          "repo": "flutter",

dev/try_builders.json

@@ -181,6 +181,12 @@
          "enabled":true,
          "run_if":["examples/hello_world/**" ,"dev/**", "packages/flutter/**", "packages/flutter_driver/**", "packages/flutter_test/**", "packages/flutter_tools/lib/src/test/**", "packages/flutter_web_plugins/**", "bin/**"]
       },
+      {
+         "name":"Linux flutter_plugins",
+         "repo":"flutter",
+         "task_name":"flutter_plugins",
+         "enabled":true
+      },
       {
          "name":"Mac build_aar_module_test",
          "repo":"flutter",