Human readable output histogram: 1st column too small

[oschaaf]

As can be observed in here, the 99,9... histogram percentile bleeds over into the second column.

I suspect this crept in in a recent Envoy dep update

To resolve we should ideally:

• Don't rely on any default formatting, which might get updated by dependencies
• In addition or instead of the above, truncate the percentile precision (0.999 probably would suffice)
• Figure out how we can make sure this stays put in a test

Thanks to @jmarantz for noticing