[Feature] Improve GatewayServer declerative setup in 1.0

[EladDolev]

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

With current implementation, creating the GatewayServer resource would generate a Secret resource with a key pair unless a secret already exists.
That makes it very hard for declarative setup that uses SealedSecret for example for creating this Secret as the sealed-secrets controller would refuse to touch the Secret if it already exists, hence there's a race condition here

Describe the solution you'd like

A way of preventing automatically creating the Secret resource with a key pair when creating the GatewayServer resource

Describe alternatives you've considered

I have no alternatives other than manual intervention or manual setup which kinda beats the purpose of declarative setup

[claudiolor]

Fixed with #2747