Fixes deadletter related tickets

[tapaswenipathak]

Things related to deadletter, cli.

Closes #141.
Closes #159.
Closes #192.
Closes #193.

• Add Tests.

cc @mapbox/platform-engine-room.

[jakepruitt]

Just a note on file structure: I think rather than going with the watchbot v3 pattern of bin/cli.js and the command pattern like:

$ watchbot dead-letter ...

We should instead make watchbot-dead-letter a separate command that has an entry in the bin property of the package.json:

ecs-watchbot/package.json

Lines 9 to 12 in 09e69ee

	"bin": {
	"watchbot": "./bin/watchbot.js",
	"watchbot-log": "./bin/watchbot-log.js"
	},

With "watchbot-dead-letter": "./bin/watchbot-dead-letter.js".

Then, within ./bin/watchbot-dead-letter.js, we can have all of the logic from ./lib/dead-letter.js and the meow CLI handlers.

[jakepruitt]

Why do we need to add the ECR mappings?

[tapaswenipathak]

Per my understanding ECR is available in all regions but ecs-conex images are stored in few regions, would it be needed to define the mapping while creating a new ecs-watchbot service in a region as to where ecs-conex is writing images?

[jakepruitt]

@tapasweni-pathak ooo good catch, I didn't check line 339 of lib/template before.

[jakepruitt]

Alright, gave a shot at refactoring some of this, but there's definitely more room for improvement if you want to pick any of this up @arunasank!

[jakepruitt]

Alright, I think all of the tests are passing now. This still needs real-life tests against dead letters with messages in them before we can merge.

[arunasank]

👋 @jakepruitt Is there a reason you renamed the test/*.jest.js files to test/*.spec.js as part of this PR? We should update the snapshot updation script in package.json to account for this change.