feat: add a new plugin trigger for detecting what the current deployment method is

This is currently used solely for reporting.

Closes #3047

docs/deployment/application-management.md

@@ -169,12 +169,14 @@ dokku apps:report
 ```
 =====> node-js-app
        App dir:             /home/dokku/node-js-app
-       Git sha:             dbddc3f                  
+       Git sha:             dbddc3f
+       Deploy method:       git
 =====> python-sample
 not deployed
 =====> ruby-sample
        App dir:             /home/dokku/ruby-sample
        Git sha:             a2d477c
+       Deploy method:       git
 ```
 
 You can run the command for a specific app also.