Keptn 0.11.x Tutorials Update + Quickstart guide + New Learning path

[oleg-nenashev]

This pull request is a bulk update that produces a new version with the following goals

• [x] Update the Keptn Tutorials for the 0.11.x release which was missing before
• [x] Make 0.11.x the tutorial displayed by default. Was 0.9.x before
• [x] Link the Tutorials site to the public quickstart Guide on the Keptn website
• [x] Introduce a new learning path when tutorials start from quickstarts: Local or a Public Demo. Only after that a full tour is offered

This is a temporary implementation for the Quickstart tutorial, later a new one will be introduced along with Antora

Screenshots

Default landing:

Quickstart landing:

Quickstart tutorial:

Depends on

• https://github.com/keptn/keptn.github.io/pull/983
• https://github.com/keptn/examples/pull/215
• https://github.com/keptn/keptn.github.io/pull/988

[oleg-nenashev]

I will merge it and address issues incrementally. Thanks @johannes-b !