kubernetesapply: improve cmd timeout handling (#5221)

If the process is killed due to context timeout, it'll have a
non-zero exit code (typically 137).

In these instances, we'll let the user know the command took too
long and point them at the Tiltfile API for `update_settings` so
they can increase the timeout value if needed.

Additionally, if stdout is empty on failure (which, given that
the commands are only supposed to write YAML on success to it, it
generally will be), it won't be output, so you don't get a blank
`stdout:` in the logs.

internal/controllers/core/kubernetesapply/reconciler.go

@@ -419,8 +419,18 @@ func (r *Reconciler) runCmdDeploy(ctx context.Context, spec v1alpha1.KubernetesA
 	exitCode, err := r.execer.Run(ctx, toModelCmd(*spec.ApplyCmd), runIO)
 	if err != nil {
 		return nil, fmt.Errorf("apply command failed: %v", err)
-	} else if exitCode != 0 {
-		return nil, fmt.Errorf("apply command exited with status %d\nstdout:\n%s\n", exitCode, overflowEllipsis(stdoutBuf.String()))
+	}
+
+	if exitCode != 0 {
+		var stdoutLog string
+		if stdoutBuf.Len() != 0 {
+			stdoutLog = fmt.Sprintf("\nstdout:\n%s\n", overflowEllipsis(stdoutBuf.String()))
+		}
+		if ctx.Err() != nil {
+			// process returned a non-zero exit code (generally 137) because it was killed by us
+			return nil, fmt.Errorf("apply command timed out after %s - see https://docs.tilt.dev/api.html#api.update_settings for how to increase%s", timeout.String(), stdoutLog)
+		}
+		return nil, fmt.Errorf("apply command exited with status %d%s", exitCode, stdoutLog)
 	}
 
 	// don't pass the bytes.Buffer directly to the YAML parser or it'll consume it and we can't print it out on failure