Rename project tags to project topics

Problem to solve

To help organize projects, GitLab has project tags that can be specified in project settings. There, you can specify a series of comma-delimited terms that appear on the project overview - these can help identify like projects.

However, project tags have a few problems:

1. The name "tag" conflicts with a git tag, which is completely unrelated. We should not overload the word "tag", it has important and unique meaning in git.
2. We already have a design concept in GitLab for describing an object with defined terms that you can later search/filter by. We haven't extended labels beyond issues and epics, but there's no reason why we can't use the same/similar visual concept at the project level - they're intended to do the exact same job, just for segmenting projects. We are planning to use the Badge UI pattern for this, and we scoped off a corresponding issue via #54544 (closed).

Proposal

1. Rename "Tags" to "Topics" in the project settings.
2. Update our documentation, change project tags to project topics.

Links / references