PageHeader: Update to support @mdi/js

Created by: umpox

Previously approved in https://github.com/sourcegraph/sourcegraph/pull/38084

I had to revert it as a type error with introduced when using ForwardRefComponent

Added commits: https://github.com/sourcegraph/sourcegraph/pull/38283/commits/acbdb323e966d6762027b8676c0508df3277e770 https://github.com/sourcegraph/sourcegraph/pull/38283/commits/b18ff5c7a465bdb9e9a54513d8b40e0cd01e9445

Updates PageHeader component to support @mdi/js.

Test plan

Checked locally through sg start web-standalone. Visual tests

App preview:

• Web
• Storybook

Check out the client app preview documentation to learn more.