Admin: Make certain settings per inventory pool instead of global

[neoheat]

🚀 Feature Request

Is your feature request related to a problem? Please describe.

Settings done in /admin/settings/misc/ are applied in all inventory pools. The settings

• maximum_reservation_time
• deliver_received_order_notifications
• email_signature

It should also be possible to set the settings in the individual inventory pools.

Describe the solution you'd like

It should be possible to set the settings in the individual inventory pools.

• enable the settings above to manage in an inventory pool
• write migration script for the enabled configurations
• adapt mail logic for settings (deliver_received_order_notifications,email_signature)
• adapt maximum reservation time in reservation logic and output in borrow
• rewrite automated tests