KAFKA-17014: ScramFormatter should not use String for password

[mingdaoy]

https://issues.apache.org/jira/browse/KAFKA-17014

Update saltedPassword, generateCredential, and normalize to use char[] for password handling

Gradle Test Run :clients:test > Gradle Test Executor 3 > ScramFormatterTest > rfc7677Example() PASSED
Gradle Test Run :clients:test > Gradle Test Executor 3 > ScramFormatterTest > saslName() PASSED

ScramParserTest:

[github-actions[bot]]

This PR is being marked as stale since it has not had any activity in 90 days. If you would like to keep this PR alive, please leave a comment asking for a review. If the PR has merge conflicts, update it with the latest from the base branch.

If you are having difficulty finding a reviewer, please reach out on the [mailing list](https://kafka.apache.org/contact).

If this PR is no longer valid or desired, please feel free to close it. If no activity occurs in the next 30 days, it will be automatically closed.

[github-actions[bot]]

This PR has been closed since it has not had any activity in 120 days. If you feel like this was a mistake, or you would like to continue working on it, please feel free to re-open the PR and ask for a review.