Report Argon2 crypto backend version in debug output

For Argon2 native code (gcrypt, OpenSSL) a flag in debug output is printed.

If libargon is used, then [cryptsetup libargon2] is printed (embedded code) or [external libargon2] for dynamic external library.

Crypto backend (OpenSSL 3.0.11 19 Sep 2023 [default][legacy] [external libargon2])

or

Crypto backend (OpenSSL 3.0.11 19 Sep 2023 [default][legacy] [cryptsetup libargon2])

Fixes: #851 (closed)