Support of post-quantum algorithms

#### Feature Description

Post-quantum algorithms are getting more and more traction from a technical (RFCs, actual adoption [1], support in common implementations [2]) and regulatory standpoint (ANSSI timeline in France, US Government recommendations,…).

Consul should begin supporting post quantum algorithms such as X25519MLKEM768 for TLS key exchange (requires TLS 1.3).

If I understand correctly, TLS implementation in Consul is delegated to the tlsutil package which in turn depends on crypto/tls.

Golang does support post quantum algorithms in crypto/tls since 1.24 (https://go.dev/pkg/crypto/tls/), so Consul might already support these algorithms, but if so IMHO the documentation should reflect that.

[1] https://radar.cloudflare.com/post-quantum

[2] among others, https://openssl.foundation/news/the-features-of-3-5-post-quantum-cryptography

#### Use Case(s)

Consul TLS endpoint for KV, API Gateway,…

Start by tracing Consul's TLS handling through the tlsutil package and Go's crypto/tls support for TLS 1.3. Check whether X25519MLKEM768 is already available in the supported Go versions, then determine whether the issue requires implementation, configuration, or documentation. Done should mean a clearly scoped and validated support or documentation change.

Written by the indexing model from the issue text.