Improve Vault pod rotation

What

Improves Vault pod rotation.

• Switch readinessProbe to HTTP (instead of vault status exec)
• Reduce readiness probe interval to 3 seconds (vs 5)
• Increase readiness initialDelaySeconds to give the pods some more time to initialize
• Increase terminationGracePeriodSeconds to 30 seconds
• Fix listeners to be IPv4 (no IPv6 in the pod/cluster)
• Set externalTrafficPolicy to Local
• Forward internal ui requests to all ready pods (no just leader)
• Increase internal endpoint DNS TTL to 1h

Why

Reduce client errors during upgrades and rotations.

gitlab-com/gl-infra/production#8761 (closed)