Add user specific color setting for languages

[MizukiTemma]

Motivation

We have introduced a centralised language color assignment system which provides configuarable but inter-regionally same color-language combinations (see #2390 and #2715) to improve understandability of graphs in the statistics. However, it is not easy for everyone to distinguish all the colors each another, as we have already many languages and new ones are comming (see the conversatio in #2858).

Proposed Solution

Add a setting section where each user can configure a color for each language.

⚠️Language-color combinations which are saved by this setting should be valid and available only for the user who set it. Otherwise it contradicts to the original motivation of introducing inter-regionally fixed color-language combinations.

💡Show only languages that are relevant to the user in the setting? For region users only the languages that are used in the region, for admin users all languages?

Alternatives

Leave it as it is.

User Story

Additional Context

Design Requirements

• [ ] where to implement the setting section
• [ ] How it should look like (color picker was suggested in #2858)