Namespace for sbus scale rules

[Larocceau]

This PR closes #1188

The changes in this PR are as follows:

• Adds the field namespace to the ServiceBusScaleRule, which is used to associate the scale rule to the right sbus

I have read the contributing guidelines and have completed the following:

• [ ] Tested my code end-to-end against a live Azure subscription.
• [x] Updated the documentation in the docs folder for the affected changes.
• [x] Written unit tests against the modified code that I have made.
• [x] Updated the release notes with a new entry for this PR.
• [x] Checked the coding standards outlined in the contributions guide and ensured my code adheres to them.

If I haven't completed any of the tasks above, I include the reasons why here:

• Instead of testing on a existing deployment, I compared a ARM template of a successful implementation of this feature using a custom scale rule, with one using this feature. There was no significant difference in the two templates.

Below is a minimal example configuration that includes the new features, which can be used to deploy to Azure:

containerApp {
      ....
      add_servicebus_scale_rule "sb-keda-scale" {
          QueueName = "wishrequests"
          MessageCount = 5
          SecretRef = "servicebusconnectionkey"
          Namespace = "servicebus"
      }
}

[Larocceau]

@mattgallagher92 this is ready for review

[ninjarobot]

@Larocceau sorry for the delay, are there any updates on the docs and testing so this can get completed?

Please @ me if you need more information.

[Larocceau]

Hi @ninjarobot! Sorry for the delay; things been a bit messy for us, and I've left CIT (as has most other dev staff). I did not get around this, but would be happy to wrap this up later.