Resolve "Improve pipeline speed"

Description

Related Issue

Motivation and Context

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.

Closes #126 (closed)

Dockerfile

@@ -7,6 +7,8 @@ RUN apt-get update && apt-get install -y git
 RUN git config --global url."https://$GITLAB_USER:$GITLAB_TOKEN@code.fbi.h-da.de".insteadOf "https://code.fbi.h-da.de"
 
 WORKDIR /src/gosdn
+COPY go.* .
+RUN go mod download
 COPY . .
 RUN GOOS=linux go build $BUILDARGS ./cmd/gosdn