changed pipeline for new runner

Description

• Changed the container image build process to kaniko and separated it into 2 jobs (build testing image & build image)
• Changed and introduced variables for container images and go version
• Replaced go test with gotestsum to allow export of junit files to gitlab

Related Issue

Motivation and Context

In order to use the new runner which only uses Docker Containers (no shell runners anymore) a change in the build process was needed.
Without Docker in Docker (DinD) (which is a security risk) the build process was changed to kaniko and all related files (e.g. Dockerfile) were updated. The changed and new introduced variables (docker image, docker testing image, go version and ceos image) were done, to unify the pipeline. For example, the go version was set at different locations and not the same throughout the entire project.
In order to find failed tests faster, gotestsum is used, which allows the export of junit files to gitlab. Gitlab has a function to integrate these files into the UI (e.g. https://code.fbi.h-da.de/danet/gosdn/-/pipelines/85112/test_report)

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.