☔ Add XDS config tab to outbound and inbound view

[lahabana]

Description

For outbound it should work only with MeshService.

Now that we have predictable names for Clusters we should be able to show the XDS config for a specific outbound.

We would have a new tab next to config/stats/clusters and show just the data we are interested in. This make it a lot easier for folks to understand what the XDS config for an outbound is and to understand what could be happening.

For only do DPPs (no gateway proxies).

• add xds config tab to inbound tray #3182
• add xds config tab to outbound tray with only xds cluster
• add xds config tab to outbound tray with xds cluster and listeners
• xds tab for gateway listeners #3236
• Reflect backend decision on stats line format separator #3237

[lahabana]

Here's some XDS config for demo-app and redis:
demo-app-xds.json
redis-xds.json