* feat(highlight): extend types and constants for custom hex colours
* feat(highlight): update colour to support hex strings
* refactor(annotator): update component to accept hex colours
* feat(highlight): add colour picker with max 4 custom colors
* feat(settings): add custom colour editor with limit
* refactor: custom highlight colors can only be modified in settings
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Co-authored-by: Huang Xin <chrox.huang@gmail.com>
Huang Xin