Initial package: etcd 3.7.1 from official upstream binaries

Fedora retired etcd in rawhide, so recreate it. Instead of building from
source with the Go packaging macros, repackage the official upstream
release tarballs (x86_64 and aarch64), fetched via spectool.

Stays drop-in compatible with the former Fedora package: same package
name, /usr/bin/{etcd,etcdctl,etcdutl}, /etc/etcd/etcd.conf, /var/lib/etcd,
etcd.service and the etcd system user (sysusers.d).

Differences from the Fedora package:
- no golang-go.etcd.io-etcd-devel subpackage
- etcd.service runs /usr/bin/etcd directly (no GOMAXPROCS bash wrapper)
- etcd.conf: drop options removed upstream (proxy, debug,
  log-package-levels), add ETCD_LOG_LEVEL
- LICENSE taken from the upstream tag, release tarballs do not ship it

sources

@@ -0,0 +1,3 @@
+SHA512 (etcd-v3.7.1-linux-amd64.tar.gz) = ee1d8b79d6ac4713d2d84cf95255439eaef1d641d57d0ee510668599010aabe012a74fb027bc91fc52cf378505cb91713d399a6eebfb7b8f17755c399c94d536
+SHA512 (etcd-v3.7.1-linux-arm64.tar.gz) = d81a2047582df2569f74c304e5af1ea9cbfb47b4ca0ca607612dfec5d09613b764b2a6b8222dfb1d520bcc7b5715b16d197fede6f984265cb444ba70608230c5
+SHA512 (LICENSE) = 6bd02bb97b3976857ebc154d11f9869472328b6d7d650b9d088ed425d167391c1f5ac87b7633fd92988831d36ea0b3be8d5bb2425399dcf237a88ba14e5fe375