TLS certificate-based automatic client authentication

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**Describe the solution you'd like**
The ability to automatically map client certificates to ACL users, similar to e.g. postgresql.

**Additional context**[
Redis 8.6 recently introduced this feature.](https://redis.io/docs/latest/develop/whats-new/8-6/#tls-certificate-based-authentication)

Start by reading the linked Redis 8.6 TLS certificate-based authentication documentation and locating Dragonfly’s existing TLS, ACL, and client-authentication entry points. Compare the desired certificate-to-ACL-user mapping with current behavior; done means certificates can automatically authenticate to the intended ACL users, with coverage for the relevant authentication cases.

Written by the indexing model from the issue text.