We need to take first steps towards removing PageHeader and it's subcomponents from @carbon/react.

Context

PageHeader was initially delivered through @carbon/react. Shortly after, we decided in #19634 that it should live in @carbon/ibm-products instead.

We knew 1-2 consumers were already using it from @carbon/react, so we chose to leave it in at the time. It needs to be removed with minimal/no impact on the community.

Proposed plan

• Remove PageHeader stories
• Keep and update PageHeader.mdx "overview" page to only contain a "this has moved" message pointing consumers to @carbon/ibm-products
• Add deprecation warning to PageHeader and related components, pointing to @carbon/ibm-products
• Add a codemod to assist in updating consumers' imports to the new location, installing @carbon/ibm-products if needed.
• Remove once Telemetry shows 0 usage, or as part of v12 #15803