[Login View Enhancement] Visually Identify Self-Hosted At Login

### Problem Statement

It is common for organizations to run a self-hosted instance of Sentry as well as purchase the SAAS product.

Often the url's for these services look like this:

sentry.acme.io
acme.sentry.io

Troubleshooting Auth issues with either service can be complicated when evaluating the service at a glance - URLs aren't often raised in screenshots either.

### Solution Brainstorm

Visually differentiate the login view of self-hosted Sentry.