Reduce image size

[gatheluck]

Why

In #71, we plan to move poetry install process into Docker image build step without considering cache created by poetry, and it will increase image size. In this ticket, we try to find unnecessary files (cache etc.) and remove them to reduce image size.

Definition of Done

• Docker image size is reduced by removing unnecessary files.

How

• Use https://github.com/wagoodman/dive to find unnecessary files.
• Remove them in side of Docker image build step.