As a first-time user, I want to discover burndown charts more easily
### Problem to solve
I watched a video by @victorwu and saw burndown charts, THEN realised I didn't know how to find them. Mousing-around the UI
did not show any label saying 'burndown' nor progress. Eventually I found them.
As a first-time user, I think they should be more discoverable.
### Further details
I recorded [a video ](https://youtu.be/MLG4YBl8Dfc)so you can see where I looked, as a new user, in CE.
### Proposal
I'd suggest a boring UI solution such as:
* making the milestone number an obvious clickable link (blue, underlined), or
* making the green progress bar links which take you to the burndown chart
* enabling expired/past project buttons click to burndown chart, as they do for active/future projects.
gitlab-ce~2975006 gitlab-ce~2278651 gitlab-ce~3103451 gitlab-ce~2024184
issue