[FR] Have "enabled" for online stores

### Willingness to contribute

No. I cannot contribute a bug fix at this time.

### Feature Request Proposal

For offline configs, there's a config to enable the offline store. We should do the same for online store.

### Motivation

> #### What is the use case for this feature?
For offline configs, there's a config to enable the offline store. We should do the same for online store.

### Details

_No response_

### What component(s) does this feature request affect?

- [ ] `Python Client`: This is the client users use to interact with most of our API. Mostly written in Python.
- [ ] `Computation Engine`: The computation engine that execute the actual feature join and generation work. Mostly in Scala and Spark.
- [ ] `Feature Registry API`: The frontend API layer supports SQL, Purview(Atlas) as storage. The API layer is in Python(FAST API)
- [ ] `Feature Registry Web UI`: The Web UI for feature registry. Written in React