build: fix build details link in experimental mode

[crazy-max]

fixes #2382

Temp workaround while we are working on cleaning up the controller logic.

[tonistiigi]

what's the difference?

[crazy-max]

seems to handle the attached session when monitoring:

buildx/commands/build.go

Line 466 in d353f5f

ref = be.Ref

will be "local" for local builds:

buildx/controller/local/controller.go

Line 24 in d353f5f

ref: "local",

[tonistiigi]

Can we rename this "kind" or "type" then?

[crazy-max]

Looking a bit more at it, for local builds with controller it always set local but for remote it sets a random id that lives across the controller session:

buildx/controller/remote/client.go

Line 120 in 746eadd

ref := identity.NewID()

So ref is still good but confusing as this is not a build ref. It's even more confusing as we already have BuildOptions.Ref in

buildx/controller/pb/controller.proto

Line 80 in 746eadd

string Ref = 29;

I renamed it to sessionID.