"attributes" settings are completely ignored for LDAP configuration
### Summary
When configuring LDAP via the gitlab_rails['ldap_servers'] option, the "attributes" block in the settings is completely ignored. See also https://forum.gitlab.com/t/ldap-first-name-and-last-name-ignored/8720 and https://gitlab.com/gitlab-org/gitlab-ee/issues/361.
### Steps to reproduce
Chose any field for "username", "email", "first_name", "last_name" or "name" and reconfigure the application. The data filled in in the user profile form that appears after a successful login is always the same: "username" maps to "uid", "email" to "mail", name to "cn".
Anonymized example configuration in which the "attributes" block is ignored:
`
gitlab_rails['ldap_servers'] = YAML.load <<-'EOS'
main: # 'main' is the GitLab 'provider ID' of this LDAP server
label: 'LDAP'
host: 'ldap.example.net'
port: 636
uid: 'uid'
method: 'ssl'
bind_dn: ''
password: ''
active_directory: false
allow_username_or_email_login: false
block_auto_created_users: true
base: 'ou=people,dc=example,dc=net'
user_filter: ''
attributes:
username: 'shortName'
email: 'preferredMail'
first_name: 'firstName'
last_name: 'lastName'
name: ''
EOS
`
### What is the current *bug* behavior?
The attributes block is ignored. The default attribute mappings are used.
### What is the expected *correct* behavior?
The configured attribute mappings are used.
issue