Allow ExistingSecrets for cluster key

[markus-mnm]

I am attempting to remove secrets from the chart values.
For the cluster key, I found that this can be done by using an existing "to_be_replaced_by_cluster_key" placeholder which the manager init files replace.
https://github.com/wazuh/wazuh-docker/blob/c893d86b4a3dff604832cbe1e9b1c760edcb4b59/build-docker-images/wazuh-manager/config/etc/cont-init.d/0-wazuh-init#L161

Here is my approach
main...markus-mnm:wazuh-helm:feature/cluster-key-secret

[kinseii]

Here is my approach main...markus-mnm:wazuh-helm:feature/cluster-key-secret

Could you make PR?