Refactor engine workflow

[olblak]

• Improve error handling.
• Move source, condition, target to separated packages
• Refactor target schema, SCM is not anymore under YAML spec

   appVersion:
     name: "Chart appVersion"
     kind: yaml
     spec:
       file: "charts/jenkins-wiki-exporter/Chart.yaml"
       key: appVersion
-      message: "[updatecli][jenkins-wiki-exporter] Helm chart appVersion updated"
-      scm: "github"
-      repository:
+    scm:
+      github:
         user: "updatecli"
         email: "updatecli@olblak.com"

Closes: #11