[BUGFIX] Show always Install Tool's login form if permanently enabled

If the file `ENABLE_INSTALL_TOOL` with the content `KEEP_FILE` is
available, the login form must be shown instead of the template
`ShowEnableInstallToolFile`.

Additionally the button to lock the Install Tool is switched to a
warning instead.

Resolves: #85656
Releases: master, 9.5
Change-Id: I3aed824d099f23b48be0bed890935b9d244953b0
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/63831


Tested-by: Markus Klein <markus.klein@typo3.org>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Susanne Moog <look@susi.dev>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Susanne Moog <look@susi.dev>