Fine Performance Metrics Dashboard nice-to-haves

[crusaderky]

• Part of Fine performance metrics meta-issue #7665
• Follow-up to Fine performance metrics: Bokeh dashboard #7679

The new dashboard view for Fine Performance Metrics (#7725) could use some tweaking:

• Please add a plot for gather_dep (title: "Receive data, by activity"). It's not quite redundant with get_data, as for example it can highlight deserialization-specific issues.
• The bytes plot, as it is, is not very useful. The reason is that memory-read is going to eclipse everything else. The purpose of that metric is to compare it to disk-read and calculate cache hit ratios; nothing else. It would become instantly more useful if there was a filter by activity so that it can be excluded (just like the filter by prefix).

EDIT: delivered in #7910

• The stacked bar charts could use a vertical axis
• The pie charts could use an indication of percentage in the tooltip