[FIX] DOCKER COMPOSE BUILD: added postgresql-client, updated README with docker steps, added google_auth_oauthlib to requirements.txt

[Neer-Pathak]

Description

This pull request fixes Docker build issues and updates documentation.
Specifically, it:

• Adds postgresql-client to the Dockerfile to ensure database utilities (pg_isready, etc.) are available during container build and entrypoint execution.
• Adds google_auth_oauthlib to requirements.txt to resolve missing module errors during build.
• Updates README.md to include proper Docker Compose steps for running Horilla.

Ticket Link

#887

Summary of Changes

• Updated Dockerfile: added postgresql-client to apt-get install
• Updated requirements.txt: added google_auth_oauthlib
• Updated README.md with Docker Compose instructions

Additional implementation details

• Ensured Docker image builds successfully with docker compose build.
• Verified docker compose up runs Horilla and PostgreSQL containers correctly.
• No breaking changes to existing manual installation steps.

Deployment Notes

• Docker Compose users can now run docker compose up without modifying Dockerfile or requirements manually.
• No additional deployment steps required.

Screenshot

N/A

Before

• Docker build failed due to missing postgresql-client.
• Build failed due to missing google_auth_oauthlib.
• README did not include simple Docker Compose instructions.

After

• Dockerfile includes postgresql-client → builds correctly.
• google_auth_oauthlib included in requirements → build succeeds.
• README now has clear Docker Compose instructions; users can run docker compose up directly.