Infra: Remove hard-coded API key and take from environment.

[ryan-roemer]

• [x] Remove hard coded key from here https://github.com/FormidableLabs/aws-lambda-dogs/blob/master/src/server/index.js#L28
• [x] Provide new instructions to generate a new key in README
• [x] Add key to 1password for each existing stage.
• [x] Add support for getting the api key via probably environment variable all the way to lambda (probably via serverless custom config and env vars).
• [x] Fail the deploy if key is not present.
• [x] Add instructions to README of correctly getting a key from 1password and providing the key during deploys

[keithcom]

changes have been merged and new deploys made with api keys from 1Password