LG-10074: Make usps enrollment email address configurable

[sheldon-b]

🎫 Ticket

LG-10074

🛠 Summary of changes

• Adds a new configuration value for the email address that we send to USPS when we create USPS enrollments
• Begins using the new configuration value, including falling back to 'no-reply@login.gov' if the configuration value is set to empty string

[sheldon-b]

This spec file has gotten pretty loose; I'm planning to submit a follow-up PR that refactors this file. Just an FYI

[NavaTim]

Looks good, LGTM.

[NavaTim]

The fallback isn't necessary with the fallback configuration in place (though you'll need to update the test if you accept this change).

Suggested change

	email: IdentityConfig.store.usps_ipp_enrollment_status_update_email_address.presence ||
	'no-reply@login.gov',
	email: IdentityConfig.store.usps_ipp_enrollment_status_update_email_address,

[sheldon-b]

I was on the fence about it myself -- it's only useful if someone accidentally edits the config and specifies an empty string for the email address. And even then it will be a kind of sneaky intervention. Yet it's still a pretty common pattern (example) for there to be a hard-coded default on top of the configuration default.

I'll go ahead with your suggestion. Also going to start a thread in slack to hear other folks' thoughts on if there's a good reason to have the hard-coded default