Want to pass additional data in "items" beside test-result counts and not show them all on same pie chart

### What feature do you want to see added?

Our JSON test summaries are parsed from maven verdicts lines and include the time consumption of a test.

Currently the plugin treats all numbers equally, so the pie chart has (say) a small section for 10 passed tests and big section for 200 sec the tests took to execute - which is not really useful. It also displays the info in a table, which is helpful to compare different suites (maybe notice run-away tests that had to time out) and gauge evolution over time.

This RFE is about choosing the best idea to move forward. Notably it seems partially overlapped with earlier issues like #55

* Note: actual timings are fractional like "123.45s" - per #108 I suppose they are rounded/truncated to integers, not ignored - right?

One idea I've had was to add an optional map (similar to "color" map) to define a list of pie charts and which item keys go where (possibly some columns get represented in several charts; maybe some columns are not exposed anywhere); if this map is absent - default is to put everything on same chart as it is now.

A loose example below aims to render one chart with just the verdicts, no times:
````
{
"id": "my report",
"items": [
{ "id": "testSuite1", "results": {"passed": 3, "failed": 0, "skipped": 1, "timesec": 25} },
{ "id": "testSuite2", "results": {"passed": 8, "failed": 3, "skipped": 0, "timesec": 1200} },
{ "id": "testSuite3", "results": {"passed": 1, "failed": 0, "skipped": 4, "timesec": 5} },
{ "id": "testSuite4", "results": {"passed": 10, "failed": 0, "skipped": 0, "timesec": 250} }
],
"colors": {
"passed": "GREEN",
"failed": "RED",
"skipped": "YELLOW"
},
"charts": [
{ "id": "chart1", "keys": ["passed", "failed", "skipped"]}
]
}
````

I suppose a useful other chart would map the `id`'s of each item vs. `timesec` spent by each, so there would be a pie with 4 slices for this example, but wording that as a map may need some thinking.

Maybe if there is one entry in "keys" - iterate over "id" (or "name") of each "item" for the chart, e.g. to compare how many tests passed in each suite? This would be consistent with "Aktie/Rente" example from the README:
````
"charts": [
{ "id": "chart2", "keys": ["passed"]},
{ "id": "chart3", "keys": ["timesec"]}
]
````

Yet another useful chart could be a run-time summary to compare the total amount of tests across suites (so treated as a single "keys" with a value calculated from a list of results columns for each item), somewhat like:
````
"charts": [
{ "id": "chart4", "sum-of": ["passed", "failed", "skipped"]}
]
````
(this approach seems extensible to other predefined formulas named reasonably like `sum-of` is here).

### Upstream changes

_No response_