Add Release Callback Interface

[theory]

Right now, tweets are sent out on successful release from within the controller. There are a few problems with this, though:

• The user can get an error on tweet failure, even though upload and release was successful
• One might want to send out other notifications on successful upload (e.g., IRC, identi.ca, etc.)
• One might want to do other things on successful download, such as execute a command-line utility (e.g, pgxn_api_sync).

So create an interface for adding callbacks on successful release, but where the user doesn't get an error if any callbacks fail. They should be configurable in the configuration file, and easy to implement. Perhaps use Plack middleware as a model.

[theory]

Another suggestion from Hitoshi Harada:

• Send an email on successful release. Perhaps to a mail list?

[umitanuki]

In terms of fail tolerant system, I'd suggest MQ. But for customizability of users I don't know which direction should go.

[theory]

I'm working on this now, since I need to rip out the Twitter support anyway. Just adding a trigger to the distributions table that passes the distribution meta JSON as a payload to pg_notify(), and implementing a library to consume various notifications and dispatch to various consumers, including Twitter and Mastodon for now. Will make it pretty straightforward to add new integrations in the future by writing a pretty simple Perl module.