[BUGFIX] Doctrine: Use compatible charset name for database connection

Use the charset name 'utf8' instead of 'utf-8' for MySQL connections as
some MySQL server versions silently ignore the connection charset name
'utf-8' and work with the global default connection charset instead.
Using 'utf8' as charset name doesn't exhibit this behavior.

Also changes the silent upgrade wizard to only set the default driver
and connection charset if no value has been configured, this avoids
silently changing non-default values for these options.

Change-Id: I94e1e7c557aff890cec357ef9ee069ae9aa052c6
Resolves: #76265
Releases: master
Reviewed-on: https://review.typo3.org/48310


Tested-by: Riccardo De Contardi <erredeco@gmail.com>
Tested-by: Gianluigi Martino <gmartino27@gmail.com>
Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Frank Naegler <frank.naegler@typo3.org>
Tested-by: Frank Naegler <frank.naegler@typo3.org>