Add initial code to support unique per-entry IDs

This code has two caveats for old entries:
1. the ID is being backfiled with a random per-(device,entry) ID. So the ID won't match cross-device.
2. the server-side ID will still be a random ID that is unrelated to the entry ID

shared/testutils/testutils.go

@@ -17,6 +17,7 @@ import (
 
 	"github.com/ddworken/hishtory/client/data"
 	"github.com/google/go-cmp/cmp"
+	"github.com/google/uuid"
 )
 
 const (
@@ -326,6 +327,7 @@ func MakeFakeHistoryEntry(command string) data.HistoryEntry {
 		StartTime:               time.Unix(fakeHistoryTimestamp, 0).UTC(),
 		EndTime:                 time.Unix(fakeHistoryTimestamp+3, 0).UTC(),
 		DeviceId:                "fake_device_id",
+		EntryId:                 uuid.Must(uuid.NewRandom()).String(),
 	}
 }