feat: Allow email alerts on self-hosted deploys when using SMTP

[HeathHopkins]

Is your feature request related to a problem? Please describe.

The current behavior for self-hosted email alerts requires Resend to be configured in order to create the alert. The alert system already uses SMTP if available, so the web UI needs to be updated to consider SMTP a valid configuration.

Describe the solution you'd like to see

Modify the emailAlertsEnabled variable to check for process.env.ALERT_SMTP_HOST assignment.

Describe alternate solutions

None

Additional information

No response