Support bucket_sort aggregation

[iuriikhrystiuk]

Describe the feature:
There are multiple visualizations that allow to apply buket_script aggregations in one way or another. However, when we are talking about ordering terms in terms aggregations by the values, calculated in bucket_script, this is not allowed. There are use-cases when we need to show top terms ordered by the values calculated in the bucket_script.

Describe a specific use case for the feature:
Prerequisite: index, with documents, that contain following fields:

• effectiveDate: a date field to apply date histogram on
• tenantName: a keyword field that is used to break down visualization
• receivedCount: a double field, used in percentage calculations
• totalCount: a double field, used in percentage calculations

Use Case:
Plot percentage of receivedCount over effectiveDate daily broken down by tenantName. Order tenantName by percentage of receivedCount descending and display only top 5 tenantName values.

[elasticmachine]

Pinging @elastic/kibana-app-services (Team:AppServicesSv)

[ppisljar]

Thank you for contributing to this issue, however, we are closing this issue due to inactivity as part of a backlog grooming effort. If you believe this feature/bug should still be considered, please reopen with a comment.