Function resolve_image 

pub fn resolve_image(registry: Option<&str>, tag: &str) -> String

Resolve the full container image reference for the bindy image.

The image name is always bindy; only the registry/org prefix and tag vary:

registry	tag	result
None	latest	ghcr.io/firestoned/bindy:latest
Some("my.reg.io/org")	v0.5.0	my.reg.io/org/bindy:v0.5.0

Trailing slashes on registry are stripped before composing the reference.