[DPE-9751] add K8s services for primary and replica endpoints

[reneradoi]

This PR adds Kubernetes services for primary and replica endpoints, which can be used by clients to connect to Valkey.

Design:

• add new class K8sClient, that provides methods for creating/updating K8s services and for adding labels to pods
• add new method reconcile_k8s_services() to the Sentinel manager class that calls the K8s client methods, based on the current deployment and primary/replica setup
• the services are owned by the stateful set of the application, meaning they will be removed on application removal
• trigger the reconcile_k8s_services() on the leader unit on any peer relation change, to update the ports if required
• publish the K8s services instead of unit endpoints to client relation data on K8s

Other changes:

• add the services to DNS SANs for the TLS certificate requests
• update rust to 1.94.0 to allow building lightkube

Integration testing is covered by the existing tests for client relations. The requirer-charms will now connect via the services in the tests on K8s.

[Mehdi-Bendriss]

Thanks René! Really clean, only 1 comment from my side

[skourta]

Small comments. Thank you @reneradoi

[Mehdi-Bendriss]

Thanks René! approved, merge pending CI pass

[skourta]

Thank you @reneradoi