Add functionality to upload images to S3

This change adds the following functionality:

- Add the motion detection image to a S3 bucket.
- Pass a presigned URL linking to the image in the JSON payload of the
  MQTT event message.
- Add the possibility of customizing whether images are uploaded to a S3
  bucket or not.

Change-Id: Id82401839e92dbc62f3bbd1e7e7f0adeeb5718a6
diff --git a/go.mod b/go.mod
index 775389b..16cca89 100644
--- a/go.mod
+++ b/go.mod
@@ -7,6 +7,7 @@
 	github.com/eclipse/paho.mqtt.golang v1.3.1
 	github.com/flashmob/go-guerrilla v1.6.1
 	github.com/go-sql-driver/mysql v1.5.0
+	github.com/minio/minio-go/v7 v7.0.7
 	github.com/sirupsen/logrus v1.7.0
 	github.com/spf13/cobra v1.1.1
 	gomodules.avm99963.com/forks/parsemail v0.0.0-20210122134334-731e54968e51