Use `openssl cms -aes-256-gcm-siv`

Use cipher algorithm AES-256-GCM-SIV that does authentication over AES-256-CTR that doesn't.

See also:
https://github.com/openssl/openssl/issues/12220
https://github.com/openssl/openssl/issues/12220#issuecomment-1237509811
https://github.com/openssl/openssl/issues/24421
https://github.com/openssl/openssl/discussions/22269

https://github.com/openssl/openssl/issues/28607
https://github.com/openssl/openssl/commit/86344acb02eb3718b0491b9915846667c55c95ff

Demo:
```shell
echo "test content" > test_cms.txt
key=000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f
# NOTE: aes-256-gcm != aes-256-gcm-siv # https://www.reddit.com/r/crypto/comments/giw4wz/comment/fqi1wbh/
# We would want to use the latter!
openssl cms -encrypt -binary -aes-256-gcm -secretkey $key -secretkeyid 1234 -in test_cms.txt -out test_cms.enc
openssl cms -decrypt -binary -secretkey $key -secretkeyid 1234 -in test_cms.enc
rm -f test_cms.txt test_cms.enc
```

Start with the shell demo in the issue and inspect how this backup utility invokes OpenSSL CMS. Read the linked OpenSSL issues and commit to determine whether the required cipher is available; done means the CMS encryption and decryption flow uses AES-256-GCM-SIV rather than AES-256-GCM.

Written by the indexing model from the issue text.