Resolve "Allow selection of single PHP version"

Closes #1 (closed)

Added posibility to use specific PHP versions, comma separated

Initial functionality is preserved

--use-php=system disables the sury repository and just installs the system's default PHP version.

ommiting the argument (use all versions)

Fixing merge conflict of !1 (closed)

Until “Don't disable php8.0 as it does not exist anymore (#31 (closed))” lands in, of course that installer fails with “ Command a2dismod php8.0 mpm_prefork 2>&1 failed”. But I’ve tested with https://git.ispconfig.org/eurodomenii/ispconfig-autoinstaller/-/tree/1-php-versions-with-31-a2dismod-php8-criticial-error and it works.