✨ use ephemeral runtimes for discovered assets

We were already instantiating new runtimes for every asset that was
discovered. However, until the introduction of ephemeral runtimes, these
had the disadvantage that any runtime that was shut down would also shut
down the plug instance, which is shared.

In this new paradigm, we introduce explicitly ephemeral runtimes, which
are not shared. They have their own plugin instance that can safely be
shut down without impacting other providers.

For more details see: mondoohq/cnquery#2050

Signed-off-by: Dominik Richter <[email protected]>

policy/scan/local_scanner.go

@@ -277,7 +277,7 @@ func (s *LocalScanner) distributeJob(job *Job, ctx context.Context, upstream *up
 	for i := range assetCandidates {
 		candidate := assetCandidates[i]
 
-		runtime, err := providers.Coordinator.RuntimeFor(candidate.asset, candidate.runtime)
+		runtime, err := providers.Coordinator.EphemeralRuntimeFor(candidate.asset)
 		if err != nil {
 			return nil, false, err
 		}
@@ -419,7 +419,7 @@ func (s *LocalScanner) distributeJob(job *Job, ctx context.Context, upstream *up
 				runtime:          runtime,
 			})
 
-			// we don't need the runtime anymore, so close it
+			// shut down all ephemeral runtimes
 			runtime.Close()
 		}
 		finished = true