Consolidated CLI, dead letter management

[rclark]

Sets up a framework for a consolidated CLI, currently with 2 commands available:

> watchbot --help

  Build an AWS stack to do your work for you

  USAGE: watchbot <command> [OPTIONS]

  Commands:
    worker-capacity     assess available resources on the cluster
    dead-letter         triage messages in dead letter queue

  Options:
    -h, --help          show this help message
    -s, --stack-name    the full name of a watchbot stack
    -r, --region        the region of the stack (default us-east-1)

This incorporates @emilymdubois' worker-capacity function, and adds a command for interacting with the dead letter queue:

> watchbot dead-letter -r ap-northeast-1 -s ecs-telephone-rclark
? Would you like to: (Use arrow keys)
❯ Triage dead messages individually? 
  Print out all dead messages? 
  Return all dead messages to the work queue? 
  Purge the dead letter queue? 

These options are pretty self-explanatory. The individual triage pulls one message from the dead letter queue, prints it out for you, and asks you if you want to:

? Would you like to: (Use arrow keys)
❯ View this message's recent logs?
  Return this message to the work queue?,
  Return this message to the dead letter queue?,
  Delete this message entirely?,
  Stop individual triage?

Upon making a selection, it does that, then presents you with another dead message (if there is one).

TODO:

• fix worker capacity tests
• tests for new command
• fix CLI description text
• view recent logs for individual jobs
• spinner / progress indication on long processes
• try to improve cloudwatch log search speeds this will require some work in cwlogs.