Allow to use a CDN with S3

[tanoabeleyra]

Description

This PR allows using a CDN (e.g. AWS CloudFront) to serve the files stored in AWS S3. This is optional and backward-compatible, it will only be applied when specifying the environment variable DJANGO_AWS_S3_CUSTOM_DOMAIN.

Rationale

It's really common to use S3 with CloudFront, this setting makes it easier to achieve that.

[Andrew-Chen-Wang]

You should add in that new environment variable to the .envs/.production/.django, writing a note there, adding some docs to the docs/settings.rst, and give a little more elaboration in the settings/production.py or the env file too.

[tanoabeleyra]

Hi @Andrew-Chen-Wang, thanks for the feedback. Considering that this variable is optional, should it go in .envs/.production/.django? For instance, DJANGO_AWS_S3_REGION_NAME is optional and it isn't in the envs file.

The idea is that if the user doesn't give any value to DJANGO_AWS_S3_CUSTOM_DOMAIN it should behave like it's currently doing in master.

[Andrew-Chen-Wang]

Ah I see. The "optional" justification makes sense.

[tanoabeleyra]

Is there anything else needed for this to be merged? (cc: @browniebroke)

[browniebroke]

Thanks for this!

Is there anything else needed for this to be merged?

Nothing apart from me finding some spare time :)

[tanoabeleyra]

Hi @browniebroke. Sure, I understand, there's no rush actually, I just wanted to be sure that the changes looked ok to you.

Thanks for approving it!