Add input plugin for rollbar service. (#1247)

* Report rollbar events.

Signed-off-by: Cyril Duez <cyril@stormz.me>
Signed-off-by: François de Metz <francois@stormz.me>

* Fix indent with go fmt.

* Add test for rollbar webhooks.

* Report more data from new_item event.

* Handle new deploy webhook.

Signed-off-by: Cyril Duez <cyril@stormz.me>
Signed-off-by: François de Metz <francois@stormz.me>

* Update default port.

* Add readme.

* Add rollbar_webhooks to the readme.

* Add rollbar_webhooks to plugins list.

* Add tag level for new_item event.

* Update readme.

* Update changelog.

plugins/inputs/rollbar_webhooks/README.md

@@ -0,0 +1,47 @@
+# rollbar_webhooks
+
+This is a Telegraf service plugin that listens for events kicked off by Rollbar Webhooks service and persists data from them into configured outputs. To set up the listener first generate the proper configuration:
+```sh
+$ telegraf -sample-config -input-filter rollbar_webhooks -output-filter influxdb > config.conf.new
+```
+Change the config file to point to the InfluxDB server you are using and adjust the settings to match your environment. Once that is complete:
+```sh
+$ cp config.conf.new /etc/telegraf/telegraf.conf
+$ sudo service telegraf start
+```
+Once the server is running you should configure your Rollbar's Webhooks to point at the `rollbar_webhooks` service. To do this go to `rollbar.com/` and click `Settings > Notifications > Webhook`. In the resulting page set `URL` to `http://<my_ip>:1619`, and click on `Enable Webhook Integration`.
+
+## Events
+
+The titles of the following sections are links to the full payloads and details for each event. The body contains what information from the event is persisted. The format is as follows:
+```
+# TAGS
+* 'tagKey' = `tagValue` type
+# FIELDS
+* 'fieldKey' = `fieldValue` type
+```
+The tag values and field values show the place on the incoming JSON object where the data is sourced from.
+
+See [webhook doc](https://rollbar.com/docs/webhooks/)
+
+#### `new_item` event
+
+**Tags:**
+* 'event' = `event.event_name` string
+* 'environment' = `event.data.item.environment` string
+* 'project_id = `event.data.item.project_id` int
+* 'language' = `event.data.item.last_occurence.language` string
+* 'level' = `event.data.item.last_occurence.level` string
+
+**Fields:**
+* 'id' = `event.data.item.id` int
+
+#### `deploy` event
+
+**Tags:**
+* 'event' = `event.event_name` string
+* 'environment' = `event.data.deploy.environment` string
+* 'project_id = `event.data.deploy.project_id` int
+
+**Fields:**
+* 'id' = `event.data.item.id` int