Add an option to use preexisting secrets for connection parameters

[t0ffel]

Is your feature request related to a problem? Please describe.
I'm deploying datahub via argocd and I'm using external cloud services for elasticsearch/mysql/kafka.
Right now I need to pass the connection strings for all the services via helm values.
It would be much easier for me to specify pre-created secrets which would contain all the connection info, rather than specify via values. (It would be easier because the secrets would be autopopulated from cloud secrets with external-secrets operator)

Describe the solution you'd like
Instead of specifying

global:
  elasticsearch:
    host: ...
    port: ...
    useSSL: ..
    auth: ...

I want to specify something like:

global:
  elasticsearch:
    externalSecret: <secret_name>

where the secret contains:

host: ..
port: ...
useSSL: ..
auth: ...

Describe alternatives you've considered
n/a

Additional context
n/a