Set runner environment in context and env (actions#2518)

* Set runner environment in runner context and env

Extract runner_environment from the global context and expose in the
`github.runner` context and env as `RUNNER_ENVIRONMENT`.

Signed-off-by: Philip Harrison <philip@mailharrison.com>

* encoding.

---------

Signed-off-by: Philip Harrison <philip@mailharrison.com>
Co-authored-by: Tingluo Huang <tingluohuang@github.com>

src/Runner.Worker/JobRunner.cs

@@ -150,6 +150,11 @@ public async Task<TaskResult> RunAsync(AgentJobRequestMessage message, Cancellat
                 _runnerSettings = HostContext.GetService<IConfigurationStore>().GetSettings();
                 jobContext.SetRunnerContext("name", _runnerSettings.AgentName);
 
+                if (jobContext.Global.Variables.TryGetValue(WellKnownDistributedTaskVariables.RunnerEnvironment, out var runnerEnvironment))
+                {
+                    jobContext.SetRunnerContext("environment", runnerEnvironment);
+                }
+
                 string toolsDirectory = HostContext.GetDirectory(WellKnownDirectory.Tools);
                 Directory.CreateDirectory(toolsDirectory);
                 jobContext.SetRunnerContext("tool_cache", toolsDirectory);

src/Sdk/DTWebApi/WebApi/WellKnownDistributedTaskVariables.cs

@@ -1,10 +1,11 @@
-using System;
+using System;
 
 namespace GitHub.DistributedTask.WebApi
 {
     public static class WellKnownDistributedTaskVariables
     {
         public static readonly String JobId = "system.jobId";
         public static readonly String RunnerLowDiskspaceThreshold = "system.runner.lowdiskspacethreshold";
+        public static readonly String RunnerEnvironment = "system.runnerEnvironment";
     }
 }