Enable h2c for http handler. add https handler for http2

[elee1766]

new flag examples.

--https.enabled
--https.addr="0.0.0.0"
--https.port=443
--https.url="unix:///file.wow"
--https.cert="keyfile.cert"
--https.key="certfile.cert"

also adds support for h2c to the http handler - http2 protocol without tls.

[elee1766]

@AskAlexSharov is this panic in windows ci caused by this pr ? seems unrelated.

--- FAIL: TestProviderFuncRegistration (4.00s)
panic: close of closed channel [recovered]
	panic: close of closed channel

goroutine 8 [running]:
testing.tRunner.func1.2({0xfa7e00, 0xffccc0})
	testing/testing.go:1526 +0x24e
testing.tRunner.func1()
	testing/testing.go:1529 +0x39f
panic({0xfa7e00, 0xffccc0})
	runtime/panic.go:884 +0x213
github.com/ledgerwatch/erigon-lib/diagnostics.Context[...].func1()
	github.com/ledgerwatch/erigon-lib/diagnostics/provider.go:126 +0x26
github.com/ledgerwatch/erigon-lib/diagnostics_test.TestProviderFuncRegistration(0xc00003d6c0?)
	github.com/ledgerwatch/erigon-lib/diagnostics/provider_test.go:84 +0x184
testing.tRunner(0xc00003dba0, 0xfd6680)
	testing/testing.go:1576 +0x10b
created by testing.(*T).Run
	testing/testing.go:1629 +0x3ea

[AskAlexSharov]

i don't know - probably not