dbconsole: metric charts height and width need to be fixed while loading

**Describe the problem**

The DB Console currently has a bad UX where graph charts do not have a fixed width and height while loading when interacting a Metrics dashboard. To make matters worse, the Metrics page periodically refreshes which causes the entire page to re-render which results in graphs disappearing/shrinking while loading and then popping back into the full width/height after data loads.

**Expected behavior**
The height and width of each chart should be the same when loading the Metrics page.

**Additional data / screenshots**
This screenshot is from a v22.1 cluster, but this problem exists in v22.2 and v23.1

Jira issue: CRDB-24797

Epic CRDB-25476