Allow power supplies to be put on maintenance

[lunkwill42]

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

A user reports problems with some new switches, where there are intermittent alerts about outages in its redundant power supplies. They want to be able to place just the power supplies on maintenance while investigating, not the entire switch stack.

Describe the solution you'd like

NAV current can add Locations, Rooms, IP Devices and services to maintenance tasks. NAV should also be able to allow the user to select internal components from an IP device and add these to maintenance tasks.

Although the problem at hand is PSU specific, this function could allow for any internal component of devices to be added to a maintenance task. I.e. any entity registered in the NetboxEntity table.

Describe alternatives you've considered

The entire IP Device could be placed on maintenance, but this would suppress all other alerts from this device, including boxDown alerts.

Additional context

This is likely dependent on a solution for #2251. Adding a JS selector component for netbox entities to the current implementation of the maintenance task UI will likely slow the UI down even more. Even just a handful of IP Devices in an installation could correspond to hundreds of entities, which add up to bog down the HTML output and the resulting JS performance.