Update metrics in traefik-kubernetes.json grafana dashboard

[Sad-Soul-Eater]

What does this PR do?

Fix variables:

• entrypoint
• service

Fix panels:

• Requests per Entrypoint
• Apdex score
• Connections per Entrypoint

Motivation

In v3.0 were metrics changes, which broke some of the dashboard panels and variables.

Fixes #10691

Additional Notes

Connections per Service panel remains broken because it relies on the old traefik_service_open_connections metric, but I haven't found any other metrics that can be used to replace the old one.

[vsimon]

Hello, I ran into this issue also and I'd like to see a PR for this merged.

Looking over this PR, there are a couple improvements:

1. We should update both contrib/traefik-kubernetes.json and contrib/traefik.json files as this issue is impacting both charts. The identical changes are cleanly applicable to both.

2. We should remove the Connections per Service panel altogether because when open connections were refactored in PR Fix open connections metric #9656, the open_connections_service... metrics was removed as counting connections does not make sense at the HTTP/application level, so this panel should also be removed.

Here is a commit of this MR plus these additional changes:

645f5a1

@Sad-Soul-Eater Perhaps you can incorporate these in this PR?

[vsimon]

Thank you @Sad-Soul-Eater!

This PR LGTM. ping @jspdown @mmatur when you have a chance can you take a look please.

[vsimon]

Gentle ping, thanks.