[DOCS] Updates for navigation redesign (#68709)
* [DOCS] Updates for navigation redesign
* Getting started
* Set up text
* Discover
* Dashboard, Graph, ML, Maps, APM, SIEM, Dev tools
* Dev Tools, Stack Monitoring, Management
* Management
* Final changes
* [DOCS] Updates for navigation redesign
* [DOCS] Updates CCR monitoring screenshots
* updates SIEM screenshot and Cases overview text
* Added Brandon's APM image
* [DOCS] Refines CCR shard screenshot
* Removed merge conflict image file
Co-authored-by: lcawl <lcawley@elastic.co>
Co-authored-by: Ben Skelker <ben.skelker@elastic.co>
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