http: replace WorkQueue and threads handling for ThreadPool #873

Job	Run time
determine runners	3s
Windows native, fuzz, VS 2022	40m 26s
macOS native, no depends, sqlite only, gui	37m 8s
Windows native, VS 2022	54m 38s
macOS native, fuzz	20m 51s
test each commit	0s
Linux->Windows cross, no tests	32m 44s
lint	5m 1s
32 bit ARM, unit tests, no functional tests	22m 39s
no IPC, i686, DEBUG	55m 28s
macOS-cross to x86_64	50m 41s
macOS-cross to arm64	49m 43s
No wallet, libbitcoinkernel	32m 33s
ASan + LSan + UBSan + integer, no depends, USDT	1h 17m 37s
MSan, depends	1h 19m 22s
fuzzer,address,undefined,integer, no depends	2h 11m 15s
previous releases, depends DEBUG	38m 4s
TSan, depends, no gui	59m 6s
Alpine (musl), depends, gui	1h 2m 12s
tidy	1h 44m 49s
Windows, test cross-built	43m 17s
	16h 37m 37s

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