Add more styles for legends

### Feature Proposal

The idea is to introduce an additional styling option for legends, specifically focusing on the selection indicator. Currently, Chart.js supports a strikethrough effect to indicate selection. However, I suggest providing developers with the choice to toggle this feature on or off.

By offering this option, developers can decide whether to apply the strikethrough effect to the legend when it's selected or opt for a different visual cue. This small addition would enhance flexibility and customization capabilities within Chart.js, aligning more closely with diverse design preferences and use cases.

### Possible Implementation

_No response_