Add version access to the controller

This MR adds a version to the controller.

Description

The controllers version contains Major, Minor and Patch information. Additionally the version does provide build information like, e.g: goos, goarch, commit revision, commit timestamp and if the binary contains changes with regard to the commit.

The version can be provided through ldflags while building: go build -ldflags "-X code.fbi.h-da.de/danet/gosdn/controller/version.versionString=02.003.100" -trimpath -o ./gosdn ./controller/cmd/gosdn

Printing the version through ./gosdn version looks like this:

Related Issue

Motivation and Context

Information about the current version of a binary is good to have. But we will need this especially for the plugin registry to verify that the controller will get the plugins for a specific version.

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.