docs: Enhance Dynatrace guide for metric scenario

[a-thaler]

Description

Changes proposed in this pull request (what was done and why):

• Restructered the metric section by outlining 3 different options
• Provided more detailed instructions for all 3 options

Changes refer to particular issues, PRs or documents:

Traceability

• The PR is linked to a GitHub issue.
• New features have a milestone set.
• New features have defined acceptance criteria in a corresponding GitHub Issue, and all criteria are satisfied with this PR.
• The corresponding GitHub issue has a respective area and kind label.
• The follow-up issues (if any) are linked in the Related Issues section.
• Adjusted the documentation if the change is user-facing.
• The feature is unit-tested
• The feature is e2e-tested

[NHingerl]

I'd like to look at it again when the current suggestions are resolved.
I'm not a big fan of the stacked lists but I doubt our style guide allows h4 headlines.
Overall, this document is getting pretty complicated :D