Provide capability to use an existing Kubernetes secret for the gateway.auth.key

[LDL-GH]

Proposal

Right now we need to input the gateway.auth.key as a value in the helm chart. And the secret is created by the helm chart
However it would be nice to also be able to reference an existing secret.

Use-Case

This way the secret value can be managed separately from the helm chart.
Also the key is not visible, only the secret name.

Anything else?

No response

[tomkerkhove]

@LDL-GH I'm going to cut a release, are you planning on contributing this later on or should I wait?

[LDL-GH]

@tomkerkhove Looking at it right now, I'll let you know where I stand in an hour

[tomkerkhove]

Sounds good, thank you!

[LDL-GH]

@tomkerkhove PR is ready for review.
Just in time I hope?

[tomkerkhove]

Certainly, thank you!