Limit memory usage when loading files from S3

[RealOrangeOne]

Description of Changes Made

By default, files are always loaded into memory, regardless of their size. Now, files larger than 2MB are saves to disk instead.

I've also made a change upstream to change the default: jschneier/django-storages#1359

How to Test

Screenshots

MR Checklist

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Unit tests

• Added
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Documentation

• Updated build docs
• Updated editor guidelines (https://docs.google.com/document/d/1PAWccdQ4tfaZsrEWmpDhvP3GH5RRmBOARFVp4b-kje8/edit?usp=sharing)
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Browser testing

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Accessibility

• Automated WCAG 2.1 tests pass
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• Images are optimised and lazy-loading used where appropriate
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[engineervix]

Looks good to me, thanks @RealOrangeOne

[helenb]

@engineervix are we merging this one straight to main - it would be good to get the benefit straight away, but we'll need to update the integration branch if so.

[engineervix]

@engineervix are we merging this one straight to main - it would be good to get the benefit straight away, but we'll need to update the integration branch if so.

yes we can merge it straight to main, then update the integration branch