More auth mechanisms support

[yuzhichang]

sarama supports following SASL mechanisms:

• PLAIN
• SCRAM
• GSSAPI(Kerberos V5)
• OAUTH10A or OAUTHBEARER (I'm not sure which one)

kafka-go doesn't support GSSAPI and OAUTH currently. I wish kafka-go provides them, especially GSSAPI(Kerberos V5).

[yuzhichang]

I notice there's a branch named sasl-gssapi tries to add Kerberos support. However this branch is inactive for several months.

[achille-roussel]

There is work in progress in #598 to support GSSAPI.

Generally speaking, we are happy to provide exposure to third party packages that implement kafka-go extensions like new SASL mechanisms, but it is unlikely that we will be extending the number of authentication mechanisms that we maintain in kafka-go.