Legend controls: second pass

### User Story Description

The MVP list contained the legend panel. That panel for the MVP had minimal functionality. New functionalities need to be added, in particular:

- control orientation of the legend (horizontal / vertical)
- color palette (select from a list of palettes. Note: usually tools show both the name and a schema of the palette)
- control number of palette levels. You can control the number of levels, value at each level and exact color
- type of interpolation (linear vs log) between palette levels
- color to use for undefined value. The user should set from the color wheel or RGB
- pick the interpolation type for the palette: continuous, banded, constant

### Acceptance Criteria

Launch a VISOR session. Color one part by a variable. In the legends panel, all the new functionalities are available and work.

Save a state file. Launch a new VISOR session. Load the state file. Verify that all the legend advanced options are stored correctly.

### Additional Links

_No response_

### Requires new or update to third party ? If "yes" add the name(s) and the version(s) of the Third Party Software.

No

### Name and Version for Third Parties

_No response_

啟動一個 VISOR 工作階段，先檢查現有的圖例面板和狀態檔案工作流程。要求的方向、調色盤、層級、插值、未定義值顏色和持久化選項，在對著色變數生效並能從已儲存的狀態檔案正確重新載入時，即表示實作完成。

由索引模型根據 Issue 內容生成。