SAML: Configuration defaults, examples and dependencies (#17954)

* Add SAML configuration options

* Add crewjam/saml as a depdency

Needed as part of the enterprise SAML integration.

* Vendor github.com/stretchr/testify/require

The package require implements the same assertions as the `assert` package but stops test execution when a test fails.

vendor/github.com/stretchr/testify/require/require.go.tmpl

@@ -0,0 +1,6 @@
+{{.Comment}}
+func {{.DocInfo.Name}}(t TestingT, {{.Params}}) {
+	if assert.{{.DocInfo.Name}}(t, {{.ForwardedParams}}) { return }
+	if h, ok := t.(tHelper); ok { h.Helper() }
+	t.FailNow()
+}