Allow certs to be attached to specific processes.

[ejholmes]

Fixes #1013

With the addition of the ports key in the extended Procfile, it makes more sense to be able to attach a certificate to a process within the app, rather than the app itself. This is supported in the backend (CloudFormation scheduler), so this is just UI to expose it in the frontend.

This will allow you to attach different certificates to different processes (only 1 cert per process is allowed, since that's the case with ELB/ALB).

This should be fully backwards compatible with older emp clients. If the -p flag isn't provided, it just defaults to attaching the cert to the web proc:

$ emp cert-attach webCert -a acme-inc
$ emp cert-attach apiCert -p api -a acme-inc
$ emp apps 
acme-inc  web=webCert,api=apiCert  Aug 25 19:02

[phobologic]

👍