Closed state + Show / Hide Closed issue button

Description

You should be able to toggle the visibility of closed issues on the the issue board and their state of closed / open should be very obvious.

Proposal

Add tabs to filter through open/closed/all issues.

Tabs should default to open:

Include a red dot to indicate closed issues:

Original Proposal

Add a button / checkbox to toggle the visibility of closed issues make it obvious which issues are closed or not, when they are shown.

Links / references

cc @tauriedavis @dbalexandre @marin

This page may contain information related to upcoming products, features and functionality. It is important to note that the information presented is for informational purposes only, so please do not rely on the information for purchasing or planning purposes. Just like with all projects, the items mentioned on the page are subject to change or delay, and the development, release, and timing of any products, features, or functionality remain at the sole discretion of GitLab Inc.