feat: add partial support for composite primary keys (#252)

* feat: add partial support for composite primary keys

Currently, a single PK was getting handled. This PR attempts to
add the support for composite primary keys, so that generated methods
are predictable.

Currently, only read, list & delete are handled in the current PR.
Additional method support will be added in the upcoming PRs.

Added department user proto to demonstrate the same.

* consider field name "id" as well