[Python] Fix UTF-8 Encoding for CommissionWifi in REPL

[mrjerryjohns]

The CommissionWifi method was not correctly converting the encoding of
the passed in ssid and passphrase arguments to UTF-8 before passing it
down to the C++ layer.

[github-actions]

PR #16408: Size comparison from fe5ec84 to bb94f81

Full report (18 builds for cyw30739, efr32, esp32, k32w, linux, mbed, nrfconnect, p6, telink)

platform	target	config	section	fe5ec84	bb94f81	change	% change
cyw30739	light	cyw930739m2evb_01	(read/write)	603538	603538	0	0.0
			.app_xip_area	510636	510636	0	0.0
			.bss	75656	75656	0	0.0
			.data	596	596	0	0.0
			.rodata	0	0	0	0.0
			.text	0	0	0	0.0
	lock	cyw930739m2evb_01	(read/write)	561326	561326	0	0.0
			.app_xip_area	469952	469952	0	0.0
			.bss	74160	74160	0	0.0
			.data	560	560	0	0.0
			.rodata	0	0	0	0.0
			.text	0	0	0	0.0
	ota-requestor-no-progress-logging	cyw930739m2evb_01	(read/write)	571050	571050	0	0.0
			.app_xip_area	470028	470028	0	0.0
			.bss	83464	83464	0	0.0
			.data	520	520	0	0.0
			.rodata	0	0	0	0.0
			.text	112	112	0	0.0
efr32	lighting-app	BRD4161A	(read only)	921384	921384	0	0.0
			(read/write)	128752	128752	0	0.0
			.bss	126744	126744	0	0.0
			.data	2008	2008	0	0.0
			.text	921376	921376	0	0.0
		BRD4161A+rpc	(read only)	950188	950188	0	0.0
			(read/write)	144708	144708	0	0.0
			.bss	142520	142520	0	0.0
			.data	2188	2188	0	0.0
			.text	950180	950180	0	0.0
	window-app	BRD4161A	(read only)	851944	851944	0	0.0
			(read/write)	126704	126704	0	0.0
			.bss	124840	124840	0	0.0
			.data	1864	1864	0	0.0
			.text	851936	851936	0	0.0
esp32	all-clusters-app	c3devkit	(read only)	961498	961498	0	0.0
			(read/write)	1395034	1395034	0	0.0
			.dram0.bss	64048	64048	0	0.0
			.dram0.data	14188	14188	0	0.0
			.flash.rodata	197888	197888	0	0.0
			.flash.text	961498	961498	0	0.0
			.iram0.text	62016	62016	0	0.0
		m5stack	(read only)	1017639	1017639	0	0.0
			(read/write)	462892	462892	0	0.0
			.dram0.bss	69576	69576	0	0.0
			.dram0.data	34016	34016	0	0.0
			.flash.rodata	227464	227464	0	0.0
			.flash.text	1012255	1012255	0	0.0
			.iram0.text	123107	123107	0	0.0
k32w	light	k32w061+release	(read/write)	700516	700516	0	0.0
			.bss	77632	77632	0	0.0
			.data	1888	1888	0	0.0
			.text	615196	615196	0	0.0
	lock	k32w061+release	(read/write)	700652	700652	0	0.0
			.bss	77624	77624	0	0.0
			.data	1908	1908	0	0.0
			.text	615320	615320	0	0.0
linux	chip-tool-ipv6only	arm64	(read only)	9767292	9767292	0	0.0
			(read/write)	476113	476113	0	0.0
			.bss	44033	44033	0	0.0
			.data	1128	1128	0	0.0
			.data.rel.ro	371824	371824	0	0.0
			.dynamic	560	560	0	0.0
			.got	55328	55328	0	0.0
			.init	24	24	0	0.0
			.init_array	192	192	0	0.0
			.rodata	493620	493620	0	0.0
			.text	8222308	8222308	0	0.0
	thermostat-no-ble	arm64	(read only)	2221188	2221188	0	0.0
			(read/write)	149809	149809	0	0.0
			.bss	65713	65713	0	0.0
			.data	1024	1024	0	0.0
			.data.rel.ro	75728	75728	0	0.0
			.dynamic	560	560	0	0.0
			.got	4352	4352	0	0.0
			.init	24	24	0	0.0
			.init_array	360	360	0	0.0
			.rodata	137956	137956	0	0.0
			.text	1863168	1863168	0	0.0
mbed	lock-app	CY8CPROTO_062_4343W+release	(read only)	6224	6224	0	0.0
			(read/write)	2352508	2352508	0	0.0
			.bss	186644	186644	0	0.0
			.data	5752	5752	0	0.0
			.text	1315108	1315108	0	0.0
nrfconnect	all-clusters-app	nrf52840dk_nrf52840	(read/write)	1155239	1155239	0	0.0
			bss	146724	146724	0	0.0
			rodata	145768	145768	0	0.0
			text	787588	787588	0	0.0
p6	all-clusters-app	default	(read/write)	2492120	2492120	0	0.0
			.bss	120072	120072	0	0.0
			.data	2632	2632	0	0.0
			.text	1450384	1450384	0	0.0
	light-app	default	(read/write)	2395704	2395704	0	0.0
			.bss	113536	113536	0	0.0
			.data	2488	2488	0	0.0
			.text	1353968	1353968	0	0.0
	lock-app	default	(read/write)	2359248	2359248	0	0.0
			.bss	113280	113280	0	0.0
			.data	2448	2448	0	0.0
			.text	1317512	1317512	0	0.0
telink	lighting-app	tlsr9518adk80d	(read/write)	895306	895306	0	0.0
			bss	87432	87432	0	0.0
			noinit	37160	37160	0	0.0
			text	632968	632968	0	0.0