INITIAL_ADMIN_EMAIL with upper case character results in Invalid email or password

[JMDirksen]

Checklist

• Have you pulled and found the error with jc21/nginx-proxy-manager:latest docker image?
  • Yes
• Are you sure you're not using someone else's docker image?
  • Yes
• Have you searched for similar issues (both open and closed)?
  • Yes

Describe the bug
When using the INITIAL_ADMIN_EMAIL environment variable with an email address with upper case characters you are not allowed to login (Invalid email or password) because it expects to find the email address with only lower case characters in the database.

Nginx Proxy Manager Version
v2.12.6

To Reproduce
Steps to reproduce the behavior:

1. Set environment variable INITIAL_ADMIN_EMAIL with an upper case character

      INITIAL_ADMIN_EMAIL: Admin@example.com
      INITIAL_ADMIN_PASSWORD: changeme

2. docker compose up
   Shows: Creating a new user: Admin@example.com with password: changeme
3. Try to login with either admin@example.com or Admin@example.com
   Result: Invalid email or password

Expected behavior
Since the rest of the application does a toLowerCase() before changing the email in the database the initial setup.js should also do a toLowerCase() on the environment variable

I've created a PR #4664