event-handler: allow DNS alternative names that don't resolve

[zmb3]

Remove the requirement that the DNS name resolves in order for it to be included in the configured certificates. This also changes the API so that IP SANs and DNS names are no longer mutually exclusive.

Closes #52981

changelog: The event handler can now generate certificates for DNS names that are not resolvable.

[hugoShaka]

LGTM, the PR is missing a changelog entry.

Have you tested the cert generation command with the change?

[zmb3]

Have you tested the cert generation command with the change?

Yes.

$ ./event-handler configure test --dns-names=localhost,example.com,zacb.doesnotexist.com --ip=127.0.0.1

Teleport event handler Not specified, use --ldflags "-X main.Version "1.0.0""

[1] Generated mTLS Fluentd certificates test/ca.crt, test/ca.key, test/server.crt, test/server.key, test/client.crt, test/client.key
[2] Generated sample teleport-event-handler role and user file test/teleport-event-handler-role.yaml
[3] Generated sample fluentd configuration file test/fluent.conf
[4] Generated plugin configuration file test/teleport-event-handler.toml

Follow-along with our getting started guide:

https://goteleport.com/docs/management/export-audit-events/fluentd/

$ cat test/server.crt | openssl x509 -text -noout | grep DNS
                DNS:localhost, DNS:example.com, DNS:zacb.doesnotexist.com, IP Address:127.0.0.1

[public-teleport-github-review-bot]

@zmb3 See the table below for backport results.

Branch	Result
branch/v15	Failed
branch/v16	Failed
branch/v17	Create PR