Prometheus: Defining a custom timerange for each query

**Why is this needed**: When designing dashboards using the Prometheus datasource, trying to compare the values over specific timeranges, there is nothing making it able to get really precise with multiple timeranges. In my case I'm trying to configure a dashboard where I can compare my service's SLA over any timerange possible, trying to get something as dynamic as possible. **What would you like to be added**: This is something that is easy to do using other datasources like Clickhouse, where in each query you specify the timerange you want to use. It would be really usefull to be able for each query where you use the Prometheus datasource to be able to specify the timerange you want to use, instead of it being the timerange defined for the whole dashboard (changing per panel using the "query options" relative time option is not enough to be able to compare precisely). **Who is this feature for?** This is for users using the prometheus datasource, needing to be able to have in a single dashboard/panel more possibilities for configuring the timeranges used by each query.