[v11.0.x] docs: update flame graph visualization

[grafana-delivery-bot[bot]]

Backport 7db41222c6bfc9ad4fb69ca58245528239d3b995 from #86615

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What is this feature?

Updates to the flame graph docs to include:

• how to configure a flame graph (video TBA)
• when to use a flame graph
• rearranging sections to match other visualization types

Why do we need this feature?

To explain to our users how to configure a flame graph easily and when to use it.

Who is this feature for?

Grafana OSS and Cloud users

Which issue(s) does this PR fix?:

Fixes #

Special notes for your reviewer:

Please check that:

• [x] It works as expected from a user's perspective.
• [ ] If this is a pre-GA feature, it is behind a feature toggle.
• [x] The docs are updated, and if this is a notable improvement, it's added to our What's New doc.