Support basic kcp-sharding in local setup

[nexus49]

Context

Currently the local setup creates a single shard platform mesh installation.

Target

• The local setup should setup a platform-mesh deployment with 2 shards (root shard plus an additional shard)
• The 2 shards need to be exposed separately next to the front-proxy that is also exposed
• Try to make use of a single etcd instance with prefixes to minimize the impact to hardware requirements

[nexus49]

related PR: https://github.com/platform-mesh/helm-charts/pull/884/changes

[simontesar]

This ticket is about extending the local-setup with a sharded setup, so that we can use it to identify problems regarding sharding with platform-mesh itself and extend the parent epic with tasks. The scope does not include making platform-mesh work with sharding yet.

• Extend the infra chart with support for extra shards
• Reuse the existing etcd, dont run extra instances per shard
• Expose all shards locally via something like https://<shard>.<kcp-api>.local so that operators can reach it. Directly accessing a shard via kubectl is not necessary right now.
• Create a kustomization that overrides the PlatformMesh-resource to run the infra-chart with an extra shard
• Create extra task-variants that include this kustomization, but don't make it a default for now