[Lens] Allow multi field "top values"

[flash1293]

Depends on #77632

Once it's possible to access the multi fields terms aggregation, this would be a nice addition for Kibana because in quite some cases, nested terms/top values are not what the user actually wants to do.

To expose this to the user, we have to answer some questions:

• UI/UX: Will there an option to pick multiple fields in a single top values dimension or will there be separate dimensions "tied together" somehow? Any affordance to the dimensions area for multi field top values?
• Consider drag/drop sensible defaults given multi field top values...when should the system automatically use this de-scoped to [Lens] multi field top values supports drag drop #111745
• How will function transitions works with multiple fields? Just pick the first one?
• If it's a single dimension with multiple picked fields, how are the terms concatenated?
• How does filtering in the chart work?
• How does formatting work?

outcomes from planning week
Multi fields top value

• Affordance 1: Additional drop target
• Affordance 2: Button/Switch next to the existing field picker to enable “multi field mode” (does not behave like this by default) CC @MichaelMarcialis
• Multiple field selects rendered below each other (like filters)
• Reorderable via drag

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)

[ghudgins]

+1 on this issue from a customer wanting to group by multiple fields in a line chart. their usecase was $environment - $servername which are stored in 2 fields on the document today. there are workarounds for this in the agg based visualizations and in runtime fields but they really wanted this to "Just work in Lens"

[flash1293]

For reference - the workaround @ghudgins mentions is either using the table vis because it allows to specify as many breakdowns as required or creating a runtime field which is doing the concatenation as a painless script, then break down using this runtime field.

[ghudgins]

+1 on this from another user.

[flash1293]

Discussed offline (joe's original comment is about rare terms)

• Warn on inaccuracies (have to transport this information through the data table) in the editor
• Put a “fix it” action in the warning to turn on rare terms for ascending sorting
• Put a “fix it” action in the warning to turn into static terms for descending sorting
• Show “rare terms” as a new entry in the option list of ranking
• What about max_doc_count? Expose to the user and see how it feels
• What about size? Expose to the user and see how it feels

Need:

• within a dimension, how to add a multi field option that still is somewhat advanced as an option (given there is a performance penalty)...can we keep the field-level controls together while not losing the need for this as something that's advanced

[ghudgins]

dropping drag/drop from scope in this issue in lieu of #111745 which we agreed we could do as a follow-on