docs: add bootstrapping example using cluster provider gardener (#18)

Co-authored-by: Maximilian Techritz <maximilian.techritz@sap.com>
Co-authored-by: Ingo Kober <37654232+In-Ko@users.noreply.github.com>
Co-authored-by: Robert Gräff <robert.graeff@sap.com>

Author: 4 people