Add name to runner context (#1312)

* Add generateIdTokenUrl as an env var

* Add generateIdTokenUrl to env vars

* Add name and runner_group to context

* No longer add runner-group

* Update runner name if needed

* Get interface instead of concrete class

* Check for nulls on ReservedAgent

* Avoid loading setting file unnecesseraly

* Only check agentName once

* Use Trace.Error when can't update settings

* Better equals and exception handling

* Update JobDispatcher.cs

* Add tests and null check

src/Runner.Worker/JobRunner.cs

@@ -106,6 +106,9 @@ namespace GitHub.Runner.Worker
 
                 jobContext.SetRunnerContext("os", VarUtil.OS);
 
+                var runnerSettings = HostContext.GetService<IConfigurationStore>().GetSettings();
+                jobContext.SetRunnerContext("name", runnerSettings.AgentName);
+
                 string toolsDirectory = HostContext.GetDirectory(WellKnownDirectory.Tools);
                 Directory.CreateDirectory(toolsDirectory);
                 jobContext.SetRunnerContext("tool_cache", toolsDirectory);