TSVB - "group on" over multiple fields / dimensions

[ryn9]

Is your feature request related to a problem? Please describe.

When using TSVB, is is not possible to "group on" over multiple fields / dimensions.
The issue is described here: elastic/kibana#33928

Describe the solution you'd like

Would like the modules updated to support "group on" over multiple fields / dimensions.

Describe alternatives you've considered

The Elastic ecosystem worked through this via use of runtime fields - which are not available in OpenSearch.

It might be possible to work on this via scripted fields - but I believe they occur only at the "last stage of a search request" - which is too late for the needed aggregations to to place. TSVB does not currently work with scripted fields.

Additional context

n/a

[ryn9]

Regarding runtime fields - its also worth noting that there are PPL Runtime Fields, but AFAIK, those cannot be used for legacy visualizations and, instead, would only be compatible with newer observability plugin visualizations

Additionally it appears there may be some work going into an OpenSearch solution similar to runtime fields - but this has yet to be seen: opensearch-project/OpenSearch#1133

[ananzh]

@seanneumann @ahopp @kgcreative what is the priority of this feature? thx