chore: Try SSA for Kamelet install only once

[astefanutti]

This PR follows up #2814 to take into account #2814 (comment).

@zregvart let me know if that corresponds to what you had in mind.

Release Note

NONE

[zregvart]

Something like this using a mutex to lock on the first write to hasServerSideApply in order to prevent multiple gorutines competing to write to it. Written from the top of my head, might not compile...

Feel free to disregard the whole idea if you think it complicates the implementation needlessly. This will have (perhaps a slight) impact on startup performance, as all goroutines will wait for the first one to complete before running.

[astefanutti]

@zregvart I've taken on your idea to use a mutex, and I've gone for using sync.Once, which encapsulates the mutex, and exposes just the right semantic for doing the SSA attempt / fallback logic only once.

Interestingly, the installation of the 137 bundled Kamelets now takes less than 200ms on my computer using Minikube, which is less than what I observed without the extra synchronisation. That being said, we're probably inside the measurement margin error, but at least the impact is either negligible or positive.

[zregvart]

Sweet!