Limit maximun number of spans for span sets

[javiermolinar]

Currently, there is no way to limit the number of spans per span set. This query is ok:

http://localhost:3200/api/search?q={}&spss=10000

This can destabilize Tempo. We should add a new config to control this. Tempo must return an error if the spss is greater than the aforementioned limit. This is similar to the limit behaviour

https://grafana.com/docs/tempo/latest/api_docs/#search

[knylander-grafana]

Thanks for thinking about docs for this config update request. :)