Describe the feature or problem you’d like to solve

I'd like to list all repositories in an organisation that have a particular topic.

Proposed solution

Add --topic to gh repo list, e.g.

$ gh repo list MyOrganisation --topic cli

How will it benefit CLI and its users?

Organisations with a large number of repositories can use topics to organise them, and filtering by a particular topic will make bulk operations easier.

Additional context

Currently this can be replicated by using --jq to filter, but the command is very slow with a large number of repositories.

I couldn't find this functionality in Repositories API documentation, so it might have to be added there first.