B2B-88: add starter kit structure and elements

packages/email-templates/src/components/header.tsx

@@ -0,0 +1,9 @@
+import { Container, Section } from '@react-email/components';
+
+export function EmailHeader(props: React.PropsWithChildren) {
+  return (
+    <Container>
+      <Section>{props.children}</Section>
+    </Container>
+  );
+}