[Enhancement] UX improvement - provide album cover placeholder when the actual cover is being downloaded

[pawelmalak]

Every time we open albums view/grid we get this flash of "unstyled content" - default album covers. It takes a while to load all of them, even on local network. With lots of albums, you can see as they get populated one by one.

This feature request proposes to provide simplified version of album cover with the initial albums data, so they can get rendered with the album grid. This can be achived by storing cover thumbnail in base64 format or by using something like blurhash.

This is how it looks in the photoview app. They use it for photos in the album but the same approach can be used for the album covers.

Updating album cover should also update its placeholder.

[ildyria]

Todo:

• : add blur_hash column to size_variants
• : add step to generate blur_hash from thumb & small
• : add console command to generate blur_hash from already existing images
• : add diagnostic info check to count number of blur_hash missing
• : insert blur_hash in thumbnail

Questions

• : add JS decoding implementation ??
• : compute base64 image & store it in DB (replace blur_hash) ??