Add S3 and HDFS repositories
[DOCS] add azure and gce discovery plugins

Clean EC2 disco doc
Add Azure disco doc
Add Google Compute Engine doc
Fix Zen doc (add `enabled` in `multicast` parameters list) - Fix #5032.
Ignore case when parsing `script_values_sorted|unique` in aggregations.

Close #5009
[DOCS] Removed the experimental label from Tribe, Hot Threads
and Completion Suggester
[DOCS] Updated migration docs for multi_field to point to copy_to