Write pre-expiration content for emails

[h-m-f-t]

Sub-issue description

Let's draft the content that users will be sent notifying them that their domain is up for renewal.

As a domain manager/org admin,
I want to be notified when my domain is expiring
So I can maintain it

As a program,
We want to maintain accurate registrant contact info
So we can ensure that domains are actively managed an not abandoned

Acceptance criteria

• Content is drafted
• Content is reviewed and finalized

Additional context

Though we're not drafting post-expiration notifications here, completing this issue may require that we sketch out what that will be said there.

[PaulKuykendall]

Moving to design parking lot for review and pointing.