[nrfconnect] Add support for nRF52840 Dongle to lighting-app

[Damian-Nordic]

Problem

nRF Connect Lighting Example can be built for nRF development kits, but not for nRF52840 Dongle although it's feasible.

Change overview

Adapt the example to work on the dongle (enable USB CDC device class for shell and logging).
Add a shell command dfu which reboots the dongle into the bootloader (to upgrade the firmware without physically pressing the reset button).

Testing

Successfully commissioned and controlled the lighting-app on nRF52840 Dongle

[github-actions]

Size increase report for "nrfconnect-example-build" from 2478e02

File	Section	File	VM
chip-shell.elf	rodata	8	8
chip-shell.elf	text	8	8
chip-shell.elf	device_handles	-8	-8
chip-lock.elf	device_handles	8	8
chip-lock.elf	rodata	8	4
chip-lock.elf	text	8	8

Full report output

BLOAT REPORT

Files found only in the build output:
    report.csv

Comparing ./master_artifact/chip-shell.elf and ./pull_artifact/chip-shell.elf:

sections,vmsize,filesize
.debug_info,0,270
.debug_loc,0,63
.symtab,0,32
.debug_frame,0,20
.debug_str,0,13
.debug_line,0,9
.debug_aranges,0,8
rodata,8,8
text,8,8
.debug_abbrev,0,-7
device_handles,-8,-8
.debug_ranges,0,-32

Comparing ./master_artifact/chip-lock.elf and ./pull_artifact/chip-lock.elf:

sections,vmsize,filesize
.debug_info,0,270
.debug_loc,0,67
.symtab,0,32
.debug_frame,0,20
.debug_line,0,13
.debug_str,0,13
.debug_aranges,0,8
device_handles,8,8
rodata,4,8
text,8,8
.debug_abbrev,0,-7
.debug_ranges,0,-32

[woody-apple]

@msandstedt @saurabhst @mspang @LuDuda ?