When adding a sector there is no "search" bar in the "NN field", we need to scroll through all the node to find the one needed.

[OlivierMorf]

Similar to the solved issue . #925

In addition:
When adding a sector, the corresponding device should exist. Would it be possible when doing the add, to search for the device, rather then add a random device name, and pull the data such as the UUID ?
Then we just have to add the attributes and set the date.

[Andrew-Dickinson]

Note for implementers: this is a shared admin page across all device types. So this change needs to be made in src/meshapi/admin/models/device.py

See the previous pull request for an example of how to change this: #927

[vvaznis]

I'll take a look at this one