Create separate sakuli docker base image

[svettwer]

As a Sakuli developer, I want to create a dedicated base image for sakuli docker containers. This would reduce the build time, development time and increase the reusability of layers when shipping images.

Acceptance criteria:

• Separate a base image containing all software and installation processes required for a sakuli installation
• Reduce the current docker image so that the only task in the build is to install sakuli in a certain version
• Change the sakuli docker build pipelines to use the new base image
• Alter container release processes to use base image

Dependency: We need more private repos on docker hub

[svettwer]

Inform @ZNicoZ as soon as this issue is in progress

[svettwer]

on hold because of new docker license

[ZNicoZ]

contacted docker support, described our situation and asked what will be possible with the new pricing model (token etc)

[julianxyz]

removed label on Hold, because we only want to use the base image for builds in the ci pipeline for now.

[svettwer]

and most important for builds during development