[ES|QL] TS Command: Make nicer error message when trying to group on metrics

[limotova]

Example query

ts k8s 
| stats s = sum(rate(network.total_bytes_in)) by network.eth0.currently_connected_clients, b = bucket(@timestamp,1hour) 
| drop s, network.eth0.currently_connected_clients 
| eval b = false

This fails with Connection refused
Some queries will succeed even if you group on non-dimension fields, but it's not supported behavior, so we should have a nicer error message if someone attempts to do this

[elasticsearchmachine]

Pinging @elastic/es-storage-engine (Team:StorageEngine)

[kkrik-es]

Nhat, I mentioned this one to Pablo to familiarize with the planner, wdyt? #134413 has some validation examples with tests.

Here, we should allow grouping on dimensions and "labels" (i.e. fields that are neither dimensions nor metrics), but not on metrics.

[dnhatn]

@kkrik-es Sure, that would be great if @pabloem is working on this!

[pabloem]

I have a fairly simple proposal to implement this here - #135223

this does not allow metric fields in timeseries aggregates at all, and instead suggests using a FROM source. Is that reasonable?

[dnhatn]

I think this is an ES|QL issue. I can reproduce it with FROM and am working on a fix.