[*] improve single query details pg dashboard (#1276)

* change queryid filter to a text box

* move sql panel to the top

* fix lag() null issue and convert to /sec rates in calls panel

* fix lag() null issue Execution time and add Execution time per call  panel

* fix lag() null issue Shared Buffers and add Shared Buffers Hit/Read per call per call panel

* fix lag() null issue Temp Bytes Read/Written and add Temp Bytes Read/Written per call panel

* fix lag() null issue and update SQL queries for Temp Bytes and I/O time calculations

* Make `$agg_interval` a multiple of `3m`

3 minutes is the default gathering interval for the `stat_statements` metric
so having `$agg_interval` a multiple of that makes it easier to define
how many data points one wants to include in a group

* use actual time as divisor in /sec queries

* Configure null values connection

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Co-authored-by: 0xgouda <gouda0x@gmail.com>

Author: Bishoywadea