Please add support for mysql_clear_password

[ryba84]

• ejabberd version: 21.01
• Erlang/OTP 21 [erts-10.2.4] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:1]
• OS: Debian 10
• Installed from: distro package

2021-05-26 09:53:17.789 [error] <0.459.0>@ejabberd_sql:log:1082 p1_mysql_auth: do_auth_switch: Unknown authentication method mysql_clear_password
2021-05-26 09:53:17.789 [error] <0.459.0>@ejabberd_sql:log:1082 p1_mysql_conn: init failed receiving data : "p1_mysql_auth: Server request switch to unknown authentication method mysql_clear_password"

Ejabberd cannot authenticate to mysql with pam authentication.