Move all avatars to profile_picture and ensure that profile_picture is included in responses

[timcowlishaw]

Needed for #166 - Currently, in various places where fablabbcn/smartcitizen-web renders a user, no profile picture is provided, leaving the default avatar showing.

I've also added a task rake import:old_avatar_images which will copy the old avatar across to the profile_picture for all users with an avatar who don't yet have a profile_picture. This will probably not do much in staging as it uses a different s3 bucket, but works well locally setting the credentials manually. When we run in production we should keep an eye on sidekiq to make sure the ActiveStorage AnalysisJobs complete successfully.

[timcowlishaw]

@oscgonfer it'd be good to get this one into production soonish too if possible as it's kinda necessary for the profile-pictures work i need to do on smartcitizen-web!

[sentry-io[bot]]

Suspect Issues

This pull request was deployed and Sentry observed the following issues:

• ‼️ ActionView::Template::Error: undefined method `profile_picture_url' for # V0::MeController#index View Issue

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