[FEATURE] Add hook to add custom TypoScript templates

This hook allows to extend the added TypoScript by adding
custom TypoScript templates (e.g. not loaded from the database)

Resolves: #79140
Releases: master
Change-Id: Ie2350c809685fdc3886f5f77761bad5124baa2bb
Reviewed-on: https://review.typo3.org/51106


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>