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_forward.go.tmpl

@@ -0,0 +1,5 @@
+{{.CommentWithoutT "a"}}
+func (a *Assertions) {{.DocInfo.Name}}({{.Params}}) {
+	if h, ok := a.t.(tHelper); ok { h.Helper() }
+	{{.DocInfo.Name}}(a.t, {{.ForwardedParams}})
+}