Generate mocks using mockgen

[Anish Adhikari]

Is your feature request related to a problem? Please describe.
Some customers require Client mocks generated using mockgen.

Proposed Solution
Generate mocks in a different directory using mockgen without replacing current ones so that this change is backwards compatible.

Additional context
Add any other context or screenshots about the feature request here.

[Wilbert Lam]

Thanks! This will come in handy for those of us using gomock/mockgen.