Legacy reference to opendistro in internal_users.yml

[cwperks]

There is a reference to opendistro in internal_users.yml as an attribute name opendistro_security_roles. This was discovered in (#1339) where a user had copied the example configuration on the documentation website which referenced opensearch_security_roles and received an Unrecognized field error when running security admin.

The documentation website has since been reverted to display opendistro_security_roles in this PR: opensearch-project/documentation-website#892.

We should revisit this area to replace the reference to the legacy opendistro.

[peternied]

Thanks for filing this, I think that this would be a good fix, but this might not be a good time to make this change.