Disable vertical sharding when scalar function is present

[yeya24]

What happened:

In Cortex, we have seen 2 bugs caused due to scalar function related to vertical sharding.

1. bug: scalar function with aggregation cause 500 cortexproject/cortex#5207 scalar(sum by (xx) (metric)) will be shardable but we cannot handle scalar type response. And the result itself is scalar type and we don't have a way to merge.

2. bug: vertical sharding doesn't work well with scalar function cortexproject/cortex#5205 Another issue but this time scalar is used to be the parameter.

What you expected to happen:

There is no bugs in vertical sharding caused by scalar. We should just disable scalar for vertical sharding to avoid any edge cases we might hit.

[yeya24]

@fpetkovski Would love to hear your opinion on this.

[fpetkovski]

Makes sense to me. If there are known bugs caused by it, I let's go ahead and disable sharding or expressions that contain scalar 👍