Expose extra users configurer option

[aarnq]

Is your feature request related to a problem? Please describe. Not really a problem, but it would be nice to be able to define static users in OpenSearch through the config file, especially now when we've added a simpler means to run the securityadmin.

Describe the solution you'd like I would like the option to append to the configurers list of users so we could define static users.

Describe alternatives you've considered Manage the users manually, which in the long run will be more work, and wouldn't allow us to benefit from the securityadmin.

Definition of done: The option to add extra users is exposed.

[Xartos]

@aarnq Could you give an example of what config that should be exposed so we can understand the size of the issue?

[aarnq]

It would add the config option opensearch.extraUsers, in the same way as we already have for extraRoles and extraRoleMappings, which would add to the list of users already created by the opensearch-configurer.