Add PKCS#10 attributes to CSR serializer #1611

Job	Run time
Validate external types appearing in public API	1m 30s
build-windows	15m 53s
build (macOS-latest, stable)	3m 26s
Build rustls-cert-gen as a standalone package	25s
build (ubuntu-latest, stable)	5m 39s
Measure coverage	5m 28s
build (ubuntu-latest, beta)	5m 33s
Format & clippy	5m 22s
build (ubuntu-latest, nightly)	5m 46s
Documentation (stable)	56s
build (ubuntu-latest, stable 7 months ago)	5m 33s
Check semver compatibility	52s
Documentation (nightly)	1m 7s
	57m 30s

Provide feedback