Add a sentry service for server-side error reporting

[sanand0]

Add a sentry: service like this.

sentry:
  dsn: ...
  # other configurations

This should set up Sentry service like this:

import sentry_sdk
from sentry_sdk.integrations.tornado import TornadoIntegration

sentry_sdk.init(
    dsn="https://6b8cdf45e85a46cd9f867db920bcae5b@o4505424418701312.ingest.sentry.io/4505424422633472",
    integrations=[TornadoIntegration()],
    traces_sample_rate=1.0,
    # other configurations
)