feat: dockerfile and github based CI build

* fixed missing error handler in main
* add injectable build string in main
* add (dynamically linked) docker build
* add github CI workflow
* add extra but useful dev files in dev folder

dev/dialoguss/sample_user.yaml

@@ -0,0 +1,3 @@
+url: http://localhost:7123
+dial: "*384*96#"
+phoneNumber: +254722123456