Add PKCS#10 attributes to CSR serializer #1628

Job	Run time
Validate external types appearing in public API	2m 7s
build-windows	14m 46s
Build rustls-cert-gen as a standalone package	1m 1s
build (macOS-latest, stable)	3m 25s
Measure coverage	5m 50s
build (ubuntu-latest, stable)	6m 18s
Format & clippy	5m 29s
build (ubuntu-latest, beta)	5m 44s
Documentation (stable)	1m 11s
Check semver compatibility	1m 1s
build (ubuntu-latest, nightly)	5m 37s
Documentation (nightly)	1m 5s
build (ubuntu-latest, stable 7 months ago)	5m 46s
	59m 20s

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