Code Generator: Add option to control the reader DB instance code generation

[vaibhav-kaushal]

Right now, the code generator builds code which can handle both a writer DB connection and a reader DB connection. In most standard cases, the user would probably be wanting to use only one DB connection which is both reader and writer, thus making the reader DB connection redundant.

We should update the code generator to make sure that the redundant code is not being generated by default.