[nrf5-demo] Add simple service discovery code for nrf5 example app

[erjiaqing]

This PR adds a temporary solution for device discovery by sending UDP broadcasts to port 23367 (just a random port) via thread.

[wgtdkp]

thanks! LGTM 👍

Just a nit:

[github-actions]

Size increase report for "gn_nrf-example-build"

File	Section	File	VM

Full report output

BLOAT REPORT

Files found only in the build output:
    report.csv

[github-actions]

Size increase report for "gn_linux-example-build"

File	Section	File	VM

Full report output

BLOAT REPORT

Files found only in the build output:
    report.csv

[github-actions]

Size increase report for "nrf-example-build"

File	Section	File	VM
chip-nrf52840-lock-example.out	.text	508	508
chip-nrf52840-lock-example.out	.bss	0	152
chip-nrf52840-lock-example.out	[LOAD #2 [RW]]	0	-4

Full report output

BLOAT REPORT

Files found only in the build output:
    report.csv

Comparing ./master_artifact/chip-nrf52840-lock-example.out and ./pull_artifact/chip-nrf52840-lock-example.out:

sections,vmsize,filesize
.debug_info,0,16194
.debug_line,0,668
.text,508,508
.debug_str,0,450
.debug_abbrev,0,320
.debug_loc,0,318
.strtab,0,211
.symtab,0,208
.bss,152,0
.debug_ranges,0,128
.debug_frame,0,64
.debug_aranges,0,16
[LOAD #2 [RW]],-4,0
.debug_macro,0,-145
[Unmapped],0,-508

[github-actions]

Size increase report for "nrfconnect-example-build"

File	Section	File	VM

Full report output

BLOAT REPORT

Files found only in the build output:
    report.csv

Comparing ./master_artifact/chip-nrf52840-lock-example.elf and ./pull_artifact/chip-nrf52840-lock-example.elf:

sections,vmsize,filesize

[github-actions]

Size increase report for "linux-example-build"

File	Section	File	VM

Full report output

BLOAT REPORT

Files found only in the build output:
    report.csv

Comparing ./master_artifact/chip-standalone-demo.out and ./pull_artifact/chip-standalone-demo.out:

sections,vmsize,filesize

[github-actions]

Size increase report for "esp32-example-build"

File	Section	File	VM

Full report output

BLOAT REPORT

Files found only in the build output:
    report.csv

Comparing ./master_artifact/chip-wifi-echo.elf and ./pull_artifact/chip-wifi-echo.elf:

sections,vmsize,filesize

[woody-apple]

I think we're eventually going to have to push this further down into the stack. Having apps/examples be aware of this level of detail feels not great...