Remove second db update confirmation screen / rework install screen contrast

[f2cmb]

• [x] I have read the CONTRIBUTING document.
• [x] I have performed a self-review of my code.

Description

• It fixes #19269

Remove second db upgrade confirmation screen. Only one validation on requirements screen now.

Screenshots (if appropriate):

modified contrast on install/update screen

For a quick test :

Simulate DB update :

UPDATE glpi_configs
SET value = '10.0.0@fakehash'
WHERE name = 'dbversion' AND context = 'core';

Simulate installation :

mv /Developer/glpi11/config/config_db.php /Developer/glpi11/config/config_db.php.bak