Test case doc - Scope failover

https://docs.google.com/document/d/1P-34apfqEUeyOwjDUcKt63oxVB9c0_2AIwr1rrAUPS8/edit#heading=h.bki0pcsuu9qt

https://github.com/openshift/openshift-docs/pull/34035#discussion_r682650535

failover can be configured by using importAsLocal and locality settings in ServiceImportSet and configuring a DestinationRule that configures failover for the service to the locality specified in the ServiceImportSet.

Capturing a conversation from slack 8/16

Rob Cernich - I commented on the PR. I think we need some input from @Jamie Longmuir as to whether or not we want to officially support this. I think it will come down to whether or not we think we can test this in time for the 2.1 release. The code is there to support it, as I mentioned in the comment, but whether or not we can get it documented and tested is something else.

Julie Stickler  - Which is why I commented it out rather than deleted it. Easy enough to restore once we figure that out. But I didn't want to hold up merging this PR while we figure that out.

Rob Cernich - sounds good

Jamie Longmuir - I think we should support the failover feature if you feel comfortable with supporting customers on it @rcernich. If not, we'll need to find a way to make it supported fairly shortly after. I think a lot of people will be looking for it.

Rob Cernich - my biggest concern is that we'll need to do some testing around it and will need to document how to make it happen

Jamie Longmuir - Could we call it tech preview and still publish the docs?

Rob Cernich - in order to expedite the release, i was thinking maybe we treat this as a hidden feature (which isn't very concealed) and update the support matrix after the release, once we can add testing/docs

Rob Cernich -i'm okay with that, but if we go that route, we should just call it "supported" and acknowledge that it may not be fully tested

Jamie Longmuir - I just know we're going to get support cases around this if we don't provide some guidance on it... we've been saying some form of HA setup would be possible to multiple customers.

Jamie Longmuir -Wouldn't that make it tech preview though? I don't know that we have a level between tech preview and GA...

Jamie Longmuir -tech preview means we'll take feedback related support cases, but we won't provide any SLA or guarantees on support. If we called it TP, my thinking is we'd look to remove that disclaimer once we've done a bit more testing or helped a customer or two on it.

Jamie Longmuir -If decide to hide the feature, I would still want the use case addressed in the docs - even to say that it's not supported yet, as I think it's something a lot of customers are looking to get from federation...even if it wasn't the original intent. We need an HA story in the docs in the bottom line.

Jamie Longmuir -@jstickler I just want to make sure this one doesn't get lost, as I think this may be the main feature people are looking for from Federation (based on customer conservations). I'm ok if our testing isn't complete and we want to put a "Tech Preview" label beside the feature (we should only be calling it GA if we're comfortable supporting customers with an SLA on it), but I do want to make sure it gets into the docs.

From e-mail 11/17/21

Specifically, the importAsLocal setting on an ImportedServiceSet can be used to create a combined set of endpoints that includes both a local service and remote service. This could be used to create a "take over" type scenario if all of the local endpoints become unavailable.