Opt-in for SQL feature store

[jjgriff93]

Is your feature request related to a problem? Please describe.
An organisation adopting FlowEHR may not wish to have a SQL server deployed and might prefer either to bring their own preferred storage, feature store, or solely use the Datalake.

Describe the solution you'd like
I would like to have SQL as an optional module in transform, which can be enabled in config like so:

transform:
  sql:

And any additional config for it (such as sizing) can then be passed into the config block.

[jjgriff93]

Moved to release 0.2