Add pve-backup-watch 0.0.1

A Go CLI that waits for a Proxmox VE vzdump backup to finish and
then restarts the guest.

- Take one or more VMIDs and poll the node's vzdump tasks via pvesh
- Handle QEMU VMs (qm) and LXC containers (pct): unlock, graceful
  shutdown with forced stop after 120s, then start
- Restart after any result by default; -only-failed restarts only when
  the backup did not finish OK, and -warn-ok treats warnings as success
- Ignore backups that finished before the tool started
- Add -dry-run, -timeout, -interval and -node options
- Exit with 0, 1 (failure or timeout) or 2 (usage error)
- Embed version, commit and build date via ldflags (VERSION file, Makefile)
- Add README and CHANGELOG

CHANGELOG.md

@@ -0,0 +1,9 @@
+# Changelog
+
+Versioning follows [Semantic Versioning](https://semver.org). The current
+version lives in the `VERSION` file and is embedded into the binary at build time.
+
+## 1.0.0
+- Initial release.
+- Waits for the vzdump task of the given VMID(s) to finish, then restarts the guest (QEMU or LXC).
+- Flags: `-dry-run`, `-timeout`, `-interval`, `-only-failed`, `-warn-ok`, `-node`, `-version`.