Feature Request: Add support for customizable legend content in RadzenChart

[franklupo]

Is your feature request related to a problem? Please describe.
Currently, RadzenChart only supports a basic legend with series names. I'm often want to show more detailed statistics (such as latest value, min, avg, max) directly in the legend for better at-a-glance interpretation of monitoring or performance charts.

Describe the solution you'd like
I would like the RadzenChart component to support an extended/customizable legend format where I can include not only the series name, but also dynamic values such as:

• Latest value
• Min
• Average
• Max

Ideally, the legend entry would support templating or data-binding to computed statistics for each series.

Describe alternatives you've considered

• Manually creating a separate table below the chart to show statistics (less user-friendly and visually disconnected).
• Using a third-party chart library that supports extended legends (losing Radzen integration and consistency).

Additional context
The screenshot below shows an example of the desired result:
A combined chart where the legend includes not only the label (e.g., CPU, IO delay) but also key metrics like Latest, Min, Avg, Max for each series.

@typeparam TItem

<RadzenTable AllowAlternatingRows="true" GridLines="DataGridGridLines.None">
    <RadzenTableHeader>
        <RadzenTableHeaderRow>
            <RadzenTableHeaderCell>@L["Counter"]</RadzenTableHeaderCell>
            <RadzenTableHeaderCell>@L["Unit"]</RadzenTableHeaderCell>
            <RadzenTableHeaderCell>@L["Latest"]</RadzenTableHeaderCell>
            <RadzenTableHeaderCell>@L["Min"]</RadzenTableHeaderCell>
            <RadzenTableHeaderCell>@L["Avg"]</RadzenTableHeaderCell>
            <RadzenTableHeaderCell>@L["Max"]</RadzenTableHeaderCell>
        </RadzenTableHeaderRow>
    </RadzenTableHeader>

    <RadzenTableBody>
        @foreach (var item in Counters)
        {
            <RadzenTableRow>
                <RadzenTableCell>@item.Name</RadzenTableCell>
                <RadzenTableCell>@item.Unit</RadzenTableCell>
                <RadzenTableCell>@GetValue(item,TypeValue.Latest)</RadzenTableCell>
                <RadzenTableCell>@GetValue(item, TypeValue.Min)</RadzenTableCell>
                <RadzenTableCell>@GetValue(item, TypeValue.Average)</RadzenTableCell>
                <RadzenTableCell>@GetValue(item, TypeValue.Max)</RadzenTableCell>
            </RadzenTableRow>
        }
    </RadzenTableBody>

</RadzenTable>

@code
{
  [Parameter] public IEnumerable<TItem> Data { get; set; } = [];
  [Parameter] public IEnumerable<LegendCounterItem> Counters { get; set; } = [];

  private enum TypeValue
  {
      Latest,
      Average,
      Min,
      Max
  }

  private string GetValue(LegendCounterItem item, TypeValue type)
  {
      var compiledSelector = item.Selector.Compile();

      var value = type switch
      {
          TypeValue.Latest => Data.Select(compiledSelector).FirstOrDefault(),
          TypeValue.Average => Data.Select(compiledSelector).DefaultIfEmpty(0).Average(),
          TypeValue.Min => Data.Select(compiledSelector).DefaultIfEmpty(0).Min(),
          TypeValue.Max => Data.Select(compiledSelector).DefaultIfEmpty(0).Max(),
          _ => 0,
      };

      return item.Formatter != null
                  ? item.Formatter(value)
                  : !string.IsNullOrEmpty(item.StringFormat)
                      ? value.ToString(item.StringFormat)
                      : value.ToString();
  }

  public record LegendCounterItem(string Name,
                                  string Unit,
                                  string StringFormat,
                                  Expression<Func<TItem, double>> Selector)
  {
      public Func<double, string>? Formatter { get; set; }
  }
}

Best regards

[akorchev]

Simply adding a Template to the legend won't be enough. The chart "measures" the size of the legend to calculate the plot area. Currently it does it by checking the text length of the items. Perhaps we need to add a new property (Width or Height depending on the position) which should be set if the user has specified the Template of the legend.