add flow-informed tuning guidance

[yaauie]

Release notes

[rn: skip]

What does this PR do?

Improves Tuning docs to use flow-metrics to inform intuition about how and why to tune what.

Why is it important/What is the impact to the user?

Increases visibility to Flow metrics so that those seeking to tune LS pipeline performance can find a useful tool.

Checklist

• ~~[ ] My code follows the style guidelines of this project~~
• ~~[ ] I have commented my code, particularly in hard-to-understand areas~~
• [x] I have made corresponding changes to the documentation
• ~~[ ] I have made corresponding change to the default configuration files (and/or docker env variables)~~
• ~~[ ] I have added tests that prove my fix is effective or that my feature works~~

How to test this PR locally

Wait for the docs gen link to be generated :)