[DOCS] Add tip for upgrade assistant (#55027)
[DOCS] Add tip for upgrade assistant (#55027)

Our upgrade docs don't mention the upgrade assistant, which can be
helpful when migrating across major versions. The docs also don't
mention deprecation logs, which can highlight other functionality that
may change.

This adds a related tip admonition to the upgrade docs.
uschindler/elasticsearch,uschindler/elasticsearch,scorpionvicky/elasticsearch,uschindler/elasticsearch,robin13/elasticsearch,nknize/elasticsearch,robin13/elasticsearch,uschindler/elasticsearch,GlenRSmith/elasticsearch,GlenRSmith/elasticsearch,gingerwizard/elasticsearch,scorpionvicky/elasticsearch,gingerwizard/elasticsearch,gingerwizard/elasticsearch,gingerwizard/elasticsearch,nknize/elasticsearch,robin13/elasticsearch,GlenRSmith/elasticsearch,nknize/elasticsearch,robin13/elasticsearch,gingerwizard/elasticsearch,gingerwizard/elasticsearch,nknize/elasticsearch,gingerwizard/elasticsearch,nknize/elasticsearch,scorpionvicky/elasticsearch,robin13/elasticsearch,GlenRSmith/elasticsearch,scorpionvicky/elasticsearch,uschindler/elasticsearch,GlenRSmith/elasticsearch,scorpionvicky/elasticsearch