Describe the bug
If you change the SNS topic name in the process function definition, the service breaks because the topic is hard-coded in the other serverless function

The HTTP API function expects an SNS topic that doesn't exist.

To Reproduce
Steps to reproduce the behavior:

1. In serverless.yml change the sns topic name here:

  cubejsProcess:
    handler: cube.process
    timeout: 630
    events:
      - sns: "\${self:service.name}-\${self:provider.stage}-process"

2. serverless deploy
3. Try to run any query (that's not already cached in Redis)

Expected behavior
The two serverless functions should always use the same SNS topic name.

Version:
[e.g. 0.4.5]

Additional context
It should be as easy as adding an environment variable to the HTTP API function that's the topic name. Something like:

custom:
  sns-topic: "\${self:service.name}-\${self:provider.stage}-process"

functions:
  cubejs:
    handler: cube.api
    timeout: 30
    environment:
      SNS_TOPIC: ${self:custom.sns-topic}
    events:
      - http:
          path: /
          method: GET
      - http:
          path: /{proxy+}
          method: ANY
  cubejsProcess:
    handler: cube.process
    timeout: 630
    events:
      - sns: ${self:custom.sns-topic}

And then read from that env variable in the HTTP API function:

const topicArn = process.env.SNS_TOPIC