Document hash migration settings via cluster manager security settings API.

In Trinity, we can enable the password hash migration for the users using a new security settings- "/settings/security/allowHashMigrationDuringAuth". It accepts true | false (default: false, in on-prem. default: true, in capella).

The setting works only when the entire cluster is on Trinity.

Please see MB-58879 for more details.

Summary:

• When the above settings is set to true and an user authenticates against the cluster_manager, if the current authInfo for an user differ from the current security settings, the user's auth info will be upgraded.

Example flow here: https://issues.couchbase.com/browse/MB-58879?focusedId=725557&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-725557