release-23.1: server: fix total latency time on sql stats call

[maryliag]

Backport 1/1 commits from #116976.

/cc @cockroachdb/release

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For the top activity tables, we have a column execution_total_cluster_seconds with the total latency of all executions of that period. This value is important because the top activity table have up to 500 rows per aggregated timestamp, so if we add all latencies from it, we won't have the total, only the total of the top. We then have a column that has that total of that hour which is based on the main table.
Previously, when making a request to the top activity table we were returning only of of those values as the total, which works as expected if your select is in a single aggregation period. The majority of requests won't be this way, so we need to add the values from all aggregated period selects.

This commit update the query for the total select to get one value from each aggregated_ts and then adding those.

Part Of CRDB-34884

Release note (bug fix): Fix value used for the total runtime on sql stats, which was using the wrong value previously, causing the UI to display values with more than 100%.

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Release justification: bug fix

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

• Backports should only be created for serious
  issues or test-only changes.
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[cockroach-teamcity]

This change is 

[mgartner]

Reviewed 2 of 2 files at r1, all commit messages.
Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @abarganier)