Rename execution.Storage to Storer to follow Go convention

Interfaces should be named like someone actively doing a thing. Thus,
instead of Storage we use Storer.

pkg/execution/execution.go

@@ -7,8 +7,8 @@ import (
 // ID is an identifier for an execution.
 type ID string
 
-// Storage stores executions.
-type Storage interface {
+// Storer stores executions.
+type Storer 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)

pkg/execution/local_storage.go

@@ -12,7 +12,7 @@ type localStorage struct {
 	executions map[ID]*dto.ExecutionRequest
 }
 
-// NewLocalStorage responds with an Storage implementation.
+// NewLocalStorage responds with an Storer implementation.
 // This implementation stores the data thread-safe in the local application memory.
 func NewLocalStorage() *localStorage {
 	return &localStorage{