promql: Update error message when using disabled PromQL experimental aggregation function

[zenador]

For these reasons:

1. The previous message hardcoded the names of the PromQL experimental functions that were aggregators, the new message does not hardcode and does not need to be updated along with any changes in the experimental aggregation functions
2. The new message specifies the function used instead of a generic message
3. The new message is more consistent with the error message given when the user tries to use a disabled PromQL experimental function that is not an aggregator

We are modifying only the fork since we want to have a different message from the original that does not mention the config flag that may not apply to Mimir. This new message is also more consistent with the original in that it specifies the function used instead of a generic message with the hardcoded names.

Follow up to https://github.com/grafana/mimir-squad/issues/2586