provide a way to try new pomerium releases

[wasaga]

Is your feature request related to a problem? Please describe.

Sometimes, users are upgrading from installations that are very old - i.e. helm based installs that may even be config operator based ones that are years old.

while user may figure out their way for stand-alone installation - i.e. picking up a separate VM, making a clone of their config file and pointing it to a different database, this is more complicated for a kubernetes environment as the deployment is cluster-wide.

Describe the solution you'd like

We may introduce a way for users to install a specific Pomerium release without affecting an existing installation. With this approach, they may migrate some of their Ingresses by setting their spec.ingressClass: pomerium-0-21-0 without disturbing their existing Pomerium installation in a cluster.

• installation namespace: pomerium => pomerium-0-21-0
• ingressClass: pomerium => pomerium-0-21-0
• global pomerium config: global => global-0-21-0
• update deployment runtime args accordingly

Describe alternatives you've considered

Explain any additional use-cases

If there are any use-cases that would help us understand the use/need/value please share them as they can help us decide on acceptance and prioritization.

Additional context

Add any other context or screenshots about the feature request here.

[Oro]

A usecase from me: I would like to upgrade the ingress controller (that I can avoid the issue you've described with an out-of-date pomerium), but atm I cannot due to pomerium/pomerium#4044 which is not yet in pomerium-ingress.
That would be solved if e.g. I were able to specify the used pomerium version. It could also be solved with coupling the releases of pomerium and pomerium-ingress (dunno how that would look like though)

Being able to use an arbitary image with pomerium-ingress would likely also help with pre-releases and PR//issue feedback (e.g. "it should be fixed in main, can you verify?")