Clarify max node setting in cluster config docs

[lzdanski]

Issue Type

Inaccurate, misleading, or out-of-date information

Links to Affected Docs

https://docs.astronomer.io/astro/manage-hybrid-clusters#configure-maximum-node-count

The Issue or Context

It would be good to update the docs to clarify that max node count = 15 is reasonable but max node count = 20 would cover a worse case scenario.

Fix or Proposed Change

Add clarification to doc

Additional Notes

https://astronomer.slack.com/archives/C015V2JFKT5/p1707764174953009

Required Reviewers

No response