feat: optional `SSLKEYLOGFILE` support #4049

Job	Run time
deny	14s
clippy	1m 23s
codegen	13s
msrv	29s
check (ubuntu-latest)	1m 41s
rustfmt	8s
check (macOS-latest)	1m 59s
test (ubuntu-latest)	1m 50s
check (windows-latest)	3m 37s
udeps	4m 15s
test (macOS-latest)	1m 47s
test (windows-latest)	3m 7s
doc-test	1m 25s
external-types	48s
Interop Tests (ubuntu-latest)	19s
semver	2m 1s
Interop Tests (macOS-latest)	37s
Interop Tests (windows-latest)	2m 24s
	28m 17s

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