refactor: use specific error for agpl and prebuilds (#17591)

Follow-up PR to https://github.com/coder/coder/pull/17458
Addresses this discussion:
https://github.com/coder/coder/pull/17458#discussion_r2055940797

coderd/prebuilds/api.go

@@ -9,7 +9,10 @@ import (
 	"github.com/coder/coder/v2/coderd/database"
 )
 
-var ErrNoClaimablePrebuiltWorkspaces = xerrors.New("no claimable prebuilt workspaces found")
+var (
+	ErrNoClaimablePrebuiltWorkspaces        = xerrors.New("no claimable prebuilt workspaces found")
+	ErrAGPLDoesNotSupportPrebuiltWorkspaces = xerrors.New("prebuilt workspaces functionality is not supported under the AGPL license")
+)
 
 // ReconciliationOrchestrator manages the lifecycle of prebuild reconciliation.
 // It runs a continuous loop to check and reconcile prebuild states, and can be stopped gracefully.

coderd/prebuilds/noop.go

@@ -27,7 +27,7 @@ type NoopClaimer struct{}
 
 func (NoopClaimer) Claim(context.Context, uuid.UUID, string, uuid.UUID) (*uuid.UUID, error) {
 	// Not entitled to claim prebuilds in AGPL version.
-	return nil, ErrNoClaimablePrebuiltWorkspaces
+	return nil, ErrAGPLDoesNotSupportPrebuiltWorkspaces
 }
 
 func (NoopClaimer) Initiator() uuid.UUID {