Fixed paragraph formatting and broken links within studio welcome email

[LianaHarris360]

Summary

Description of the change(s) you made

This PR fixes the broken links and updates the spacing between the paragraphs in the Studio welcome email. A new SITE object has been added to include the hotfixes branch, some domain variables for SITE objects have been updated, and the way the SITE_ID is retrieved within settings.py has been refactored.

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References

Fixes #3677

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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

[bjester]

I missed this, but looks like we copy and pasted the whole dictionary, not just the value for "domain"

[bjester]

Also, do you have pre-commit installed? I would have expected it to reformat this code. I actually think it's missing from the Studio README/dev setup now that I look...

[rtibbles]

There's also this outstanding issue: #2945 which means that we can't enforce the Python linting checks either.

[bjester]

@rtibbles Ah right, I forgot we talked about handling that before the websockets work...

[rtibbles]

We couldn't though, because my event log PR hadn't been merged! We'll do it once we merge the websockets work instead.

[rtibbles]

Code changes make sense to me! One question about the slideshow itself.

[rtibbles]

Thoughts on linking to a published version of the slideshow instead of the source document?
https://docs.google.com/presentation/d/e/2PACX-1vRLHvRytsoLdOCv5EMlm5_KRKYHdtwpt_FUkC3sLeW5L12Tw9KZj5GA6klbq8dQB1nVtEBGn73GZsU9/pub?start=true&loop=true&delayms=30000&slide=id.g6b950d4fd1_0_360

cc @lauradanforth

[LianaHarris360]

I think linking to a published version would be a preferable option.

[rtibbles]

I checked with @lauradanforth and she agreed! If you can update the link, then I think we're good to merge here.

[bjester]

Lets test it out on the hotfixes server