Automate updating the container image

[fniessink]

There are some recurring manual tasks that need to be performed before building and pushing to Docker Hub, which can be automated.

Recurring manual tasks are e.g.:

1. update Dockerfile
2. update external plugin list versions
3. update startup script (profile version update when language plugins were updated)

For example: (59ac0e5)

Tasks:

• Automate point 1, version bump with a tool that preferably directly creates merge requests in github
• Automate 3, so the internal plugin version are retrieved via API, profile names <plugin version>-<rulefiles date>