Rework how batch-predictor & pyfunc-server depend on merlin-sdk

[ariefrahmansyah]

Is your feature request related to a problem? Please describe.

Currently, we need to publish merlin-sdk to PyPi first before batch-predictor and pyfunc-server able to release their new Docker image version. This is because instead of depending on the local code of merlin-sdk, they specify merlin-sdk in requirements.txt, making them resolve to PyPi.

Describe the solution you'd like

batch-predictor & pyfunc-server should depends on the local code of merlin-sdk