feat(coderd): add provisioner build version and api_version on serve (#11369)

* assert provisioner daemon version and api_version in unit tests
* add build info in HTTP header, extract codersdk.BuildVersionHeader
* add api_version to codersdk.ProvisionerDaemon
* testutil.MustString -> testutil.MustRandString

testutil/rand.go

@@ -0,0 +1,17 @@
+package testutil
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/coder/coder/v2/cryptorand"
+)
+
+// MustRandString returns a random string of length n.
+func MustRandString(t *testing.T, n int) string {
+	t.Helper()
+	s, err := cryptorand.String(n)
+	require.NoError(t, err)
+	return s
+}