Decouple NestBot service with separate Docker container

[Ani07-05]

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

Currently, the NestBot Slack integration runs within the main backend service, creating tight coupling between the general backend and Slack-specific functionality. This makes it harder to:

• Scale NestBot independently based on Slack traffic
• Debug and monitor Slack-specific issues
• Deploy updates to NestBot without affecting the main backend
• Manage different resource requirements for Slack processing

Describe the solution you'd like

Create a separate Docker container for NestBot with its own service definition:

• Add dedicated nestbot service running on port 8001
• Move docs service to port 8002 to avoid port conflicts
• Update Dockerfile to use python:3.13-slim base image for smaller image size
• Add Slack-specific environment variables (DJANGO_SLACK_BOT_TOKEN, DJANGO_SLACK_SIGNING_SECRET) to the NestBot service
• Configure proper service dependencies to ensure backend migrations complete before NestBot starts

Are you going to work on implementing this?

• Yes
• No

[Ani07-05]

@arkid15r would like to work on this

[rudransh-shrivastava]

Completed in #3939