[Feature Request]: Add a "custom color" option for theme colors

Guidelines

[X] I have searched the issue tracker for open and closed issues that are similar to the feature request I want to file, without success.
[X] I have searched the documentation for information that matches the description of the feature request I want to file, without success.
[X] This issue contains only one feature request.

Problem Description

The theme color settings only have preset colors, limited to color scheme sets which get proposed in the repo.

Proposed Solution

Adding a "custom color" option (like in the profile settings) for the theme colors [base, main & secondary] would add a lot of freedom in the field of customization to the user.

Alternatives Considered

An optional "custom color" hex-value field.

Issue Labels

improvement to existing feature, new optional setting

Additional Information

No response

FreeTubeApp / FreeTube