[FEATURE] Add hook to custom header in page mod

Add an hook to allow modifying the header of a page in the page module.
This hook is called before the content of the page is rendered.

Resolves: #52579
Releases: 6.2
Change-Id: I8914f5617d1529e98b9bc2b27cdc5a4378b0a7da
Reviewed-on: https://review.typo3.org/24460
Reviewed-by: Daniel Huf
Reviewed-by: Xavier Perseguers
Tested-by: Xavier Perseguers
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn