LDAP authentication username matching appears to be case sensitive

### Current Behavior

We have the containerized Dependency Track integrated with Active Directory. In Access Management > LDAP Users we have a list of usernames that we've added. When one of those users logs in, the username they enter has to match the case exactly as we have configured here.

E.g. - A user entering this user name:


Would get an error if their username was configured this way:


The error is:


To be clear, once the user enters their username to match the case configured in Dependency Track, the login works as expected.

### Steps to Reproduce

1. Configure LDAP integration
2. In Access Management > LDAP Users, create a new user
3. Attempt to login as user using different case than how the username is configured in DTrack.

### Expected Behavior

Dependency Track should do case insensitive matching of login usernames against its list of LDAP users.

### Dependency-Track Version

4.9.1

### Dependency-Track Distribution

Container Image

### Database Server

PostgreSQL

### Database Server Version

11

### Browser

N/A

### Checklist

- [X] I have read and understand the [contributing guidelines](https://github.com/DependencyTrack/dependency-track/blob/master/CONTRIBUTING.md#filing-issues)
- [X] I have checked the [existing issues](https://github.com/DependencyTrack/dependency-track/issues) for whether this defect was already reported