Project settings: add token selector for topics

What does this MR do and why?

In the general settings of a project, you can set any topics. To do this, a comma-separated list must be entered, which is not very convenient.

Project > General settings (before MR)

This MR makes topic selection more convenient by using a token selector.

Solves #341896 (closed)

🛠 with ❤ at Siemens /cc @bufferoverflow

Screenshots or screen recordings

Project_settings_topic_selector

How to set up and validate locally

1. Visit General Settings page of a project.
2. Select topics in Naming, topics, avatar area.

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.