Rename namespace Icinga\Form to Icinga\Forms

refs #7553
Rename Icinga\Module\Setup\Form to Icinga\Module\Setup\Forms

refs #7553
Rename Icinga\Module\Monitoring\Form to Icinga\Module\Moni...\Forms

refs #7553
Let our module autloader know that we renamed our form namespaces

refs #7553
Merge branch 'bugfix/move-forms-to-forms-namespace-7553'

fixes #7553