Query exemplars field not respected

[adrapereira]

Describe the bug
When running a TraceQL metrics query with exemplars enabled, the exemplars query field value is not respected by Tempo, it always returns the amount of exemplars decided internally in Tempo.

To Reproduce
Steps to reproduce the behavior:

1. Start Tempo (2.7.0)
2. Run a metrics query {} | rate() and set the exemplars field as 3, for example

Expected behavior
In the example above I would expect to only receive 3 exemplars, but receive more.