viz: add base path for web dashboard

[WatcherWhale]

Fixes #11851 Signed-off-by: Mathias Maes [email protected]

[tscuite]

grafana also needs to consider switching uri's，Is it easy to modify? I can provide a test

https://github.com/linkerd/linkerd2/issues/12015

[WatcherWhale]

grafana also needs to consider switching uri's，Is it easy to modify? I can provide a test

#12015

This should already work, as I also changed the grafana reverse proxy in the go code

[adleong]

Closing as inactive. Please feel free to reopen if you plan to continue work on this.