Add new setting for disabled feeds: Custom color options

[RachidTagzen]

A new color customization feature for disabled feeds has been implemented.
The "Disabled Feeds" color option is now accessible within the "Customize predefined colors" group.
The default display color for disabled feeds is gray.

NB : This feature works seamlessly as a complementary addition to the other committed features, such as Strikethrough and Hide Together, these options provide users with a comprehensive set of tools to customize and manage their feed list effectively, catering to different preferences and workflows.

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