Move execution storage to new package

pkg/execution/execution.go

@@ -0,0 +1,19 @@
+package execution
+
+import (
+	"gitlab.hpi.de/codeocean/codemoon/poseidon/pkg/dto"
+)
+
+// ID is an identifier for an execution.
+type ID string
+
+// Storage stores executions.
+type Storage interface {
+	// Add adds a runner to the storage.
+	// It overwrites the existing execution if an execution with the same id already exists.
+	Add(id ID, executionRequest *dto.ExecutionRequest)
+
+	// Pop deletes the execution with the given id from the storage and returns it.
+	// If no such execution exists, ok is false and true otherwise.
+	Pop(id ID) (request *dto.ExecutionRequest, ok bool)
+}