[milestone] Add MILESTONE file

This file is newly introduced into integration.git, so we should mirror
it here. It will soon be required for proper generation of release
version numbers.

Bug: 70302
Change-Id: Ie594feeec9a5b7209feada286e76f76e54af081c
Reviewed-on: https://fuchsia-review.googlesource.com/c/infra/roller-tests/integration/+/486266
Fuchsia-Auto-Submit: Anthony Fandrianto <atyfto@google.com>
Commit-Queue: Auto-Submit <auto-submit@fuchsia-infra.iam.gserviceaccount.com>
Reviewed-by: Oliver Newman <olivernewman@google.com>
diff --git a/MILESTONE b/MILESTONE
new file mode 100644
index 0000000..d00491f
--- /dev/null
+++ b/MILESTONE
@@ -0,0 +1 @@
+1