Add auto_deploy_on field to enable auto deployment (#225)

* Add 'owner_id' field to Repo

* Fix to update owner_id when it activates a repo

* Add the handler for 'push' events to deploy automatically

* Add the doc for 'auto_deploy_on'

Author: Noah Hanjun Lee

docs/references/deploy.yml.md

@@ -18,6 +18,7 @@ Field                    |Type                     |Required  |Description
 `payload`                |*object* or *string*     |`false`   |This field is JSON payload with extra information about the deployment. 
 `production_environment` |*boolean*                |`false`   |This field specifies whether this runtime environment is production or not.
 `deployable_ref`         |*string*                 |`false`   |This field specifies which the ref(branch, SHA, tag) is deployable or not. It supports the regular expression, [re2](https://github.com/google/re2/wiki/Syntax) by Google, to match the ref. 
+`auto_deploy_on`         |*string*                 |`false`   |This field controls auto-deployment behaviour given a ref(branch, SHA, tag). It supports the regular expression, [re2](https://github.com/google/re2/wiki/Syntax) by Google, to match the ref. 
 `review`                 |*[Review](#review)*      |`false`   |This field configures review.
 
 ## Review