feat(cli): add experimental rpty command (#16700)

Relates to https://github.com/coder/coder/issues/16419

Builds upon https://github.com/coder/coder/pull/16638 and adds a command
`exp rpty` that allows you to open a ReconnectingPTY session to an
agent.

This ultimately allows us to add an integration-style CLI test to verify
the functionality added in #16638 .

cli/dotfiles_test.go

@@ -17,6 +17,10 @@ import (
 
 func TestDotfiles(t *testing.T) {
 	t.Parallel()
+	// This test will time out if the user has commit signing enabled.
+	if _, gpgTTYFound := os.LookupEnv("GPG_TTY"); gpgTTYFound {
+		t.Skip("GPG_TTY is set, skipping test to avoid hanging")
+	}
 	t.Run("MissingArg", func(t *testing.T) {
 		t.Parallel()
 		inv, _ := clitest.New(t, "dotfiles")