Guided tour: protected helm repo example

[robertgraeff]

What this PR does / why we need it:

Adds a new example to the guided tour.
The example demonstrates how to deploy a chart from a protected helm repository.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Release note:

- New example in the guided tour: protected helm repository

[gardener-prow]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all