Cover all important features with getting started guides

[StackScribe]

Goal

The Keptn documentation set should have a "Getting started" section that includes individual exercises for each use-case plus additional "Getting started" exercises for key features.

Problem

We currently have two excellent "Getting started" exercises:

• Getting started with Keptn observability
• Getting started with lifecycle management (pre-/post-deployment tasks)

We also have three old exercises based on Andi's conference presentation and example. The example is not maintained by development and these exercises are not completely hands-on. These should be updated or removed:

• Standardize observability
• Manage release lifecycle
• Custom Keptn metrics

We also have the original "Getting started" exercise put together in December 2022 to use the podtato-head example. It does not walk the user through all steps required for implementation, instead providing scripts that do some of the more complex configuration. It has been removed from the documentation set.

DoD

One "Getting started" section that includes:

• [x] Getting started with Keptn observability
• [x] Getting started with. lifecycle management (pre-/post-deployment tasks)
• [ ] Getting started with Keptn metrics
• [ ] Getting started with Keptn evaluations (may be incorporated into another exercise)
• [ ] Getting started with Keptn analytics
• [ ] Tutorials section removed from docs
• [ ] All getting started exercises removed from Intro section
• [ ] Each "Getting started" exercise linked from the "Intro" description of that feature" and from relevant "User guide" sections

### Tasks
- [ ] https://github.com/keptn/lifecycle-toolkit/issues/2234
- [ ] https://github.com/keptn/lifecycle-toolkit/issues/2235
- [ ] https://github.com/keptn/lifecycle-toolkit/issues/2236
- [ ] https://github.com/keptn/lifecycle-toolkit/issues/2203

[mowies]

I think we could revisit this epic but in a different way. We could have guides for all of the above suggestions but not as getting started guides and rather just in the guides section on the docs page. WDYT @StackScribe ?