feat: reintroducing thumbnails

[RoccoSmit]

PR to cover the Image Preview issue
#3685

Design specs:

• Thumbnails should reside in the local file system as an optional cache.
• Only attempt to access the thumbnail when requested, and if it doesn't exist, create it and then return it.

Changes made:

• Updated api request signature to allow for a thumbnail query string variable
• Followed the logic from the previous resource flow resource/resource.go with these notable exceptions
  • The resource request will look for a thumbnail first and return it if found, rather than load the original image first then generate the thumbnail after. This limits the number of larger images being read from disk.
  • Newly generated thumbnail images are converted to byte arrays on the fly and returned, removing the need to write images to the disk and then reading them back to get the byte array.
• Moved thumbnail logic into its own file as it gets used across services
• Added thumbnail deleting logic in individual services. Resource files are deleted in the store logic, but no version of thumbnails have db related data so store logic did not feel like the place to put thumbnail file deletion.

Notes:

• The first load of the home / resource pages after this feature is enabled will cause stress on the system as each image request will attempt to generate a thumbnail. Subsequent loads should be improved as thumbnails will load.
• These changes were manually tested with sqlite and local storage storage options and work as expected

[johnnyjoygh]

LGTM, otherwise