Cache the number of each component type assigned to devices/VMs

[jeremystretch]

Proposed Changes

Add the following integer fields to dcim.Device:

• _console_port_count
• _console_server_port_count
• _power_port_count
• _power_outlet_count
• _interface_count
• _front_port_count
• _rear_port_count
• _device_bay_count
• _inventory_item_count

Add the following integer fields to virtualization.VirtualMachine:

• _interface_count

These fields would be automatically populated upon creating/modifying/deleting the relevant child components.

Justification

• Enables efficient filters of devices/VMs based on whether a certain type of component has been created.
• Eliminates the need for additional queries e.g. when display the device view.

[jeremystretch]

This might also be a use case for CTE; see #6587.

[AndMrzv]

I also like to verify that devices match their device type templates (you know something's up if a 24port 1PSU switch suddenly has 29 interfaces and 3 power ports). So maybe you'll find it useful to add same data to device types, maybe expand the idea to strict matching devices to their types or syncing (now I do this with API and Bash).

[ryanmerolle]

pushed to 3.6 milestone