Add property to configure cert authentication role

[aram535]

I'm setting up an cert authentication but can't seem to find the option value to set for the cert auth name.

https://docs.spring.io/spring-cloud-vault/docs/current/reference/html/#common-application-properties doesn't seem to contain any entries for the cert auth other than the mount name.

For Vault:

curl -H "X-Vault-Request: true" -H "X-Vault-Token: $(vault print token)" https://127.0.0.1:8200/v1/auth/cert/certs?list=true

Reference: https://github.com/spring-projects/spring-vault/pull/780

Per @mp911de ... it is settable via:

ClientCertificateAuthenticationOptions.builder().role(…).build()

[mp911de]

Another reference: https://github.com/spring-projects/spring-vault/issues/864