Create new-format (deb822) Debian .sources file

deb822.md

1. Download a Release.key file if there's no key file in a keyring yet, and save it into a .gpg file.
2. gpg --import /path/to/file
3. The above command will display key ID. Use it to export as an armored key: gpg --export --armor <keyid>
4. Create a .sources file, indenting the key and the endmarker with one space and prefixing it with a line containing a dot (.). Example:

Types: deb
URIs: http://download.opensuse.org/repositories/home:/Alexx2000/xUbuntu_25.04/
Suites: /
Components:
Signed-By: -----BEGIN PGP PUBLIC KEY BLOCK-----
 .
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 e+8BrHy9BIOXG3FrgIJvqe1PDuo4iapQ1dZ0bTFqvIsuxt1jMws2lxs2rtZuIrxx
 5lLImDuSZ48GWJMWvmCuZyjg1zvFV0WffJ5V5AAu2/ojdwbwWNDI2TAmWT6Ldy2v
 m8apMlfRa6o2MLAnlMZW0jPwVm2ggWTaPPgISkmFUaOUbLsjvIh5rBlFr03H7T8q
 LXVb7Awtwlq7EkdA0NneFGqWC+eC5DqLxKExI5Jw8BoUNZVvI1RBqARjr2DoeQ9t
 QiG8O3Fvvs4gqlFviteEWr+vzeEAbvfpeRTlABEBAAG0PmhvbWU6QWxleHgyMDAw
 IE9CUyBQcm9qZWN0IDxob21lOkFsZXh4MjAwMEBidWlsZC5vcGVuc3VzZS5vcmc+
 iQE+BBMBAgAoBQJoKsIcAhsDBQkUZVazBgsJCAcDAgYVCAIJCgsEFgIDAQIeAQIX
 gAAKCRBhUItgwzqJJYu/B/wJnAL+BLALxnvuvfhRwmHLI/Bt5Mau8myzAoQQ7jCn
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 VR2nO8i3xxkEoaKabC/mA2yMPVLmCjbqsUUx/M8xXAsWAtEy2+f/dZhxfIcUsD1Z
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 15CAuVKoqRVlTQCRYfBMbeGrW4423eDDm57ytpZz/priiEYEExECAAYFAlfkG2kA
 CgkQOzARt2udZSOZbgCff07dY2beWm9YcTw9RaCiCz+i9A8An2tIK6/ARfYVSabA
 hU2cu1KIa7Ya
 =bHV3
 -----END PGP PUBLIC KEY BLOCK-----