[TASK] Optimize I/O for configuration migration detection

Move the file_exists checks around to execute
those only if really needed.

The bootstrap methods are executed whenever
the Core does any action, so its footprint should
be as slim as possible.

Resolves: #100013
Related: #99744
Releases: main
Change-Id: I7d947c5d5b5aab52fec2610a7e6f9a030d1080c0
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/77929


Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Stefan Bürk <stefan@buerk.tech>