Add named project snapshots

src/domain/errors/project-snapshot-name-conflict.error.ts

@@ -0,0 +1,11 @@
+export class ProjectSnapshotNameConflictError extends Error {
+  constructor(
+    readonly projectId: string,
+    readonly snapshotName: string
+  ) {
+    super(
+      `Project ${projectId} already has a snapshot named "${snapshotName}".`
+    );
+    this.name = "ProjectSnapshotNameConflictError";
+  }
+}