Set thread bakends for pigweed rpc builds

[andy31415]

These are needed because of the sleep/yield functionality and are enforced in new pigweed builds.

They are not strictly required in current pigweed version, but will make updating to newer version easier (so just pulling latest pigweed works better).

This should fix things like:

https://github.com/project-chip/connectedhomeip/actions/runs/4280636928/jobs/7452659286

...
INFO    ../../examples/lighting-app/linux/third_party/connectedhomeip/third_party/pigweed/repo/pw_rpc/endpoint.cc:41:15: error: static assertion failed: PW_RPC_YIELD_MODE is PW_RPC_YIELD_MODE_SLEEP (pw::this_thread::sleep_for()), but no backend is set for pw_thread:sleep. Set a pw_thread:sleep backend or use a different PW_RPC_YIELD_MODE setting.
1206
INFO       41 | static_assert(false,
1207
INFO          |               ^~~~~
1208
INFO    ../../examples/lighting-app/linux/third_party/connectedhomeip/third_party/pigweed/repo/pw_rpc/endpoint.cc: In function ‘void pw::rpc::internal::YieldRpcLock()’:
1209
INFO    ../../examples/lighting-app/linux/third_party/connectedhomeip/third_party/pigweed/repo/pw_rpc/endpoint.cc:85:20: error: ‘chrono’ does not name a type
1210
INFO       85 |   static constexpr chrono::SystemClock::duration kSleepDuration =

[github-actions]

PR #25350: Size comparison from af511d7 to 8355b5e

Full report (1 build for cc32xx)

platform	target	config	section	af511d7	8355b5e	change	% change
cc32xx	lock	CC3235SF_LAUNCHXL		0	0	0	0.0
			(read only)	642601	642601	0	0.0
			(read/write)	203688	203688	0	0.0
			.ARM.attributes	44	44	0	0.0
			.ARM.exidx	8	8	0	0.0
			.bss	197088	197088	0	0.0
			.comment	194	194	0	0.0
			.data	1480	1480	0	0.0
			.debug_abbrev	930126	930126	0	0.0
			.debug_aranges	87280	87280	0	0.0
			.debug_frame	299812	299812	0	0.0
			.debug_info	20256131	20256131	0	0.0
			.debug_line	2656120	2656120	0	0.0
			.debug_loc	2797440	2797440	0	0.0
			.debug_ranges	281768	281768	0	0.0
			.debug_str	3023104	3023104	0	0.0
			.ramVecs	780	780	0	0.0
			.resetVecs	64	64	0	0.0
			.rodata	105761	105761	0	0.0
			.shstrtab	232	232	0	0.0
			.stab	204	204	0	0.0
			.stabstr	441	441	0	0.0
			.stack	2048	2048	0	0.0
			.strtab	377825	377825	0	0.0
			.symtab	256224	256224	0	0.0
			.text	534716	534716	0	0.0