LdapData helper

[woodseowl]

A helper for retrieving Cornell University LDAP data. Based on the legacy App\Helpers\LDAP::data() class that exists on various Cornell Laravel sites.

This PR does the following

• Adds src\Ldap\LdapData for retrieving data from LDAP
• Adds src\Ldap\LdapDataServiceProvider to provide default configuration
• Updates .env.example with required LDAP variables
• Documentation and rudimentary testing

To Review:

• Review README file additions to assess usage
• Review how the LDAP data is normalized in src\Ldap\LdapData::make(). This was based on a comparison of approaches applied in DailyCheck, IT Gov, and EMNPhone. (Improvements and alternate use case requirements welcome!)

Notes
The testing fixtures are real data from LDAP that I scrubbed of personal identifiers. I felt that this rudimentary testing was necessary to assure that we don't break how we retrieve this data that users will see as very personal.