Add filtering to the explore page
Problem
In #420804 (closed), we discovered that the explore page isn't particularly useful for exploring open source projects to contribute to in GitLab. There's too much content, and not enough ways to properly narrow it all down.
Proposal
Adding in a proper filtered search to this page, along the lines of what's on the issue or MR list page, would be a great step forward here. In the context of searching for projects to contribute to, filters for language and topic would be especially important.
Additional discussion in #420804 (comment 1504253055)