feat(backend): spawn the notifications service + basic test

[ntindle]

We want to send emails on a schedule, in response to events, and be expandable without being overbearing on the amount of effort to implement. We also want this to use rabbitmq and be easy for other services to send messages into.

This PR adds the first use of the service to simply show a log message

Changes 🏗️

• Adds a new backend service for notifications
• Adds first notification into the service -> Agent Execution
• Adds spawning the notification service

Also

• Adds RabbitMQ to CI so we can test stuff
• Adds a minor fix for one of the migrations that I thought was causing failures, but isn't but the change is still useful

Checklist 📋

For code changes:

• I have clearly listed my changes in the PR description
• I have made a test plan
• I have tested my changes according to the test plan:
  • Built and ran an agent and ensured the following log line appeared which shows the event would have sent an email

  2025-02-10 15:52:02,232 INFO  Processing notification: user_id='96b8d2f5-a036-437f-bd8e-ba8856028553' type=<NotificationType.AGENT_RUN: 'AGENT_RUN'> data=AgentRunData(agent_name='CalculatorBlock', credits_used=0.0, execution_time=0.0, graph_id='30e5f332-a092-4795-892a-b063a8c7bdd9', node_count=1) created_at=datetime.datetime(2025, 2, 10, 15, 52, 2, 162865)
  

For configuration changes:

• .env.example is updated or already compatible with my changes
• docker-compose.yml is updated or already compatible with my changes
• I have included a list of my configuration changes in the PR description (under Changes)

None of the other ports are configurable via .env.example listing so left as is

Examples of configuration changes

• Changing ports
• Adding new services that need to communicate with each other
• Secrets or environment variable changes
• New or infrastructure changes such as databases

[itsababseh]

Passed CI, multiple reviewed already and @ntindle gave the green light.