Create one-off email to notify users about Terms of Use update

[suecarmol]

Description

Created the templates, signal, and task to send a one-off email to notify users about the terms of use update.

Rationale

Our Terms of Use specify that we will update users when we make substantive changes to it. The new library user experience whereby there is just one criterion for accessing the library requires a substantive change, so we need to notify users.

Phabricator Ticket

T286897

How Has This Been Tested?

Screenshots of your changes (if appropriate):

Types of changes

What types of changes does your code introduce? Add an x in all the boxes that apply:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Minor change (fix a typo, add a translation tag, add section to README, etc.)

[Samwalton9]

Will this email send in the user's chosen language (where a translation has been completed)? I notice it doesn't have a lang parameter, which some other emails do.

[jsnshrmn]

Looks good! 😎

[suecarmol]

Will this email send in the user's chosen language (where a translation has been completed)? I notice it doesn't have a lang parameter, which some other emails do.

I didn't think about that. @jsnshrmn, will the email be sent in a user's preferred language without passing a lang parameter?

[jsnshrmn]

Will this email send in the user's chosen language (where a translation has been completed)? I notice it doesn't have a lang parameter, which some other emails do.

You are absolutely correct that we need to add that in. We can do a followup pass to catch that, but for now, we at least have the strings merged for translation.