New manage: introduce new role inventory pool manager

[neoheat]

🚀 Feature Request

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

Currently, there is no specific role restrict to manage the settings of a inventory pool, any lending manager can change the base information of a inventory pool. Because we'll move the functions in /manage/manage into admin and want to restrict the admin access to inventory managers or lending managers, this new role should have access to the settings in admin.

Describe the solution you'd like

• introduce a new role inventory pool manager
• the hierarchie of this role is below role leihs admin and above inventory manager
• restrict access to manage/manage to roles below inventory pool manager