Support for Migrating Existing etcd Clusters to etcd-druid Managed Clusters

[seshachalam-yv]

How to categorize this issue?

/area control-plane
/area auto-scaling
/area high-availability
/kind enhancement

What would you like to be added:

Implement functionality in etcd-druid that allows new etcd-druid managed members to seamlessly join an existing unmanaged etcd cluster.

Why is this needed:

Several etcd users are interested in adopting etcd-druid for its enhanced management capabilities, including automated backups and lifecycle management. However, they currently operate existing etcd clusters that are not managed by etcd-druid.

To encourage the adoption of etcd-druid, it is crucial to provide a seamless transition path for users to migrate their existing etcd clusters to be managed by etcd-druid. This support will allow the existing etcd clusters to join the etcd-druid managed cluster, and after successfully joining, old members (unmanaged by etcd-druid) can be removed by the operator.

This feature will enable users with existing etcd setups to leverage etcd-druid's management capabilities without needing to setup a new cluster from scratch, thereby facilitating smoother transitions and broader adoption of etcd-druid.