Hard-coded upgrade instructions link isn't quite right

Right now, `mn_settings_notifications.html` has a hard-coded link to a URL for upgrade instructions:

```http://phonehome.hq.couchbase.com:8091/ui/index.html#/settings/cluster?commonBucket=customer_addresses&scenarioZoom=minute&scenario=zxppkfjkm:~:text=Upgrade%20Instructions```

For any recent version of Couchbase server, this leads to:

```https://docs.couchbase.com/server/7.0/install/upgrade.html```

However, those upgrade instructions are out-of-date compared to the latest, which is at:

```https://docs.couchbase.com/server/current/install/upgrade.html```

I suggest that the hard-coded URL should be that last one.