issue 3208: welcome new user email feature added

[bjester]

Summary

Adds new registration welcome email.

Description of the change(s) you made

• Originally started by @vishalpandeyvip
• Updates all translations in templates to use newly documented {% translate ... instead of {% trans ...

Manual verification steps performed

1. Ran the devserver with SEND_USER_ACTIVATION_NOTIFICATION_EMAIL=1 env variable
2. Created a new account
3. Followed activation link
4. Extracted the email html and viewed it in a web browser

Screenshots (if applicable)

Browser screenshot:

References

#3305

Comments

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Contributor's Checklist

PR process:

• If this is an important user-facing change, PR or related issue the CHANGELOG label been added to this PR. Note: items with this label will be added to the CHANGELOG at a later time
• If this includes an internal dependency change, a link to the diff is provided
• The docs label has been added if this introduces a change that needs to be updated in the user docs?
• If any Python requirements have changed, the updated requirements.txt files also included in this PR
• Opportunities for using Google Analytics here are noted
• Migrations are safe for a large db

Studio-specifc:

• All user-facing strings are translated properly
• The notranslate class been added to elements that shouldn't be translated by Google Chrome's automatic translation feature (e.g. icons, user-generated text)
• All UI components are LTR and RTL compliant
• Views are organized into pages, components, and layouts directories as described in the docs
• Users' storage used is recalculated properly on any changes to main tree files
• If there new ways this uses user data that needs to be factored into our Privacy Policy, it has been noted.

Testing:

• Code is clean and well-commented
• Contributor has fully tested the PR manually
• If there are any front-end changes, before/after screenshots are included
• Critical user journeys are covered by Gherkin stories
• Any new interactions have been added to the QA Sheet
• Critical and brittle code paths are covered by unit tests

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Reviewer's Checklist

This section is for reviewers to fill out.

• Automated test coverage is satisfactory
• PR is fully functional
• PR has been tested for accessibility regressions
• External dependency files were updated if necessary (yarn and pip)
• Documentation is updated
• Contributor is in AUTHORS.md

[radinamatic]

No changes in strings per se, a part from the new ones in the welcome email, just the trans > translate, so seems good to go! 👏🏽

[pcenov]

I am receiving the email successfully but I noticed the following issues:

1. The first couple of links are not working/broken.
2. There is no spacing between the paragraphs.

[bjester]

@pcenov Could you forward the email to me?