Add DigitalOcean inventory plugin

Intended to complement the recently added digital_ocean module.

plugins/inventory/digital_ocean.ini

@@ -0,0 +1,25 @@
+# Ansible DigitalOcean external inventory script settings
+#
+
+[digital_ocean]
+
+# The module needs your DigitalOcean Client ID and API Key.
+# These may also be specified on the command line via --client-id and --api-key
+# or via the environment variables DO_CLIENT_ID and DO_API_KEY
+#
+#client_id = abcdefg123456
+#api_key = 123456abcdefg
+
+
+# API calls to DigitalOcean may be slow. For this reason, we cache the results
+# of an API call. Set this to the path you want cache files to be written to.
+# One file will be written to this directory:
+#   - ansible-digital_ocean.cache
+#
+cache_path = /tmp
+
+
+# The number of seconds a cache file is considered valid. After this many
+# seconds, a new API call will be made, and the cache file will be updated.
+#
+cache_max_age = 300