Support for passphrase protected keys

When using a password-protected key, MariaDB server can not start because the server waits for a key to be entered:

Enter PEM pass phrase:

Since this doesn't work if server is started as a service or as background process, an additional option --ssl-passphrase should be implemented (as in Connector/C).

Update, 17 Feb 2025

We take OpenSSL approach, where --passin/passout parameters to the command line tool can specify a file ("file:" prefix), environment variable ("env:" prefix) , clear-text password("pass:" prefix)

Note, that if ssl_passphrase is reevaluated on FLUSH SSL. That means for file-based passphrase (ssl_passphrase=file:/path/to/pass.txt), that the file will be re-read during FLUSH SSL.