[FEATURE]: Spikelines in scatterternary plots

Hi,

Description

It would be great if we could add spikelines to scatterternary plots, mapping to the a,b,c axes in an analogous way to the spikelines in a scatter plot.

Why should this feature be added?

Adding this feature would help the students we support become proficient in reading data off this plot type.

{
  "ternary": {
    "aaxis": {
      "showspikes": true,
      "spikecolor": "",
      "spikedash": "",
      "spikemode": "",
      "spikesnap": "",
      "spikesthickness": ""
    },
    "baxis": {
      "showspikes": true,
      "spikecolor": "",
      "spikedash": "",
      "spikemode": "",
      "spikesnap": "",
      "spikesthickness": ""
    },
    "caxis": {
      "showspikes": true,
      "spikecolor": "",
      "spikedash": "",
      "spikemode": "",
      "spikesnap": "",
      "spikesthickness": ""
    }
  }
}

Many thanks!

首先比较现有 scatter plot 的 spikeline 行为与 scatterternary plot 对 a、b 和 c 轴的处理方式。完成标准是 scatterternary plot 支持所请求的 spike 设置，并显示类似于 scatter plot 的 spikeline。