Too long datacenter drop down is cutoff

### Overview of the Issue

The datacenter dropdown in the Consul web UI does not scroll if there are more datacenters than can fit on screen. The only way to switch to those datacenters is either reducing the brower's font size, or editing the URL to jump to the desired datacenter.

### Reproduction Steps

Steps to reproduce this issue/view the area for improvement, eg:

1. Create at least 6-7 Consul datacenters and federate them
2. Make your browser window as short as possible. With default text size, only 5 will fully appear on screen, with the 6th slightly visible, and the 7th completely offscreen
3. In the Consul web UI, click the dropdown next to the Consul logo to show selectable datacenters

### Describe the solution you'd like

I'd like this dropdown to either scroll, and/or support some filtering component so I can filter the on-screen datacenters.

### Consul Version
1.10.8

### Browser and Operating system details

Chrome, 101.0.4951.41 (Official Build) (arm64), macOS 12.3.1