workload: fix quantile values in openmetrics exporter

[sambhav-jain-16]

hdrHistogram library has quantiles in percentages rather than absolute
values. Openmetrics standard forces the quantiles values in summary
metric to be absolute values b/w 0 and 1 inclusive.
https://github.com/prometheus/OpenMetrics/blob/296468bc2359ebac83f24301b54a0871f2268016/specification/OpenMetrics.md?plain=1#L294

Earlier the exporter would export the percentage value, this change
intends to make it absolute to adhere to openmetrics standard

Epic: none

Release note: None

[cockroach-teamcity]

This change is 

[herkolategan]

Which other tests use 50.0 vs. 0.5? Curious as the OpenMetrics standard seems to suggest this format: https://github.com/prometheus/OpenMetrics/blob/main/specification/OpenMetrics.md#summary-1

[sambhav-jain-16]

Which other tests use 50.0 vs. 0.5? Curious as the OpenMetrics standard seems to suggest this format: https://github.com/prometheus/OpenMetrics/blob/main/specification/OpenMetrics.md#summary-1

Every other tests using the workload binary and exporting the histogram summaries from it eg tpcc, ycsb etc.
Actually I checked and looks like this needs to be fixed in the openmetrics exporter itself rather than here.

I'm using expfmt.MetricFamilyToOpenMetrics from prometheus library so I assumed it will emit in right format. Looks like I was wrong.
I'll push the fixes in the workload binary in this PR itself. Thanks @herkolategan for pointing out.