Incorrect Typescript interface for SASLAuthenticate handler (custom mechanisms)

[Drew-Kimberly]

Describe the bug
The Typescript interface is defined as:

  saslAuthenticate: <ParseResult>(
    request: SaslAuthenticationRequest,
    response?: SaslAuthenticationResponse<ParseResult>
  ) => Promise<ParseResult | void>

While the implementation expects a single arg that is a wrapper object with request and response properties: https://github.com/tulios/kafkajs/blob/master/src/broker/saslAuthenticator/index.js#L42

Expected behavior
The TS interface should match the implementation

Observed behavior
Implementing a custom SASL mechanism to the TS interface will result in an error at runtime due to the unexpected shape of the arg.

[Drew-Kimberly]

Much appreciated for the fast turnaround 🙏