If you go to Settings (in the upper-right corner) and select Variables, we can add a new pod variable:
Besides the name of the variable, we set its type as query to obtain its values from a Prometheus http_request_duration_microseconds_bucket query. We then set /.*pod="([^"]*).*/ as the regex that will extract the pod label value from each observation.
Recall that each Prometheus observation has the format <metric_name>{<lbl1>=<lbl1_val>,<lbl2>=<lbl2_val>,...} <value> <timestamp>.
The pod variable can assume distinct values of the pod label, but because we also selected the Include All option, we may say that the ...
