add API to RAIS for clearing cache

[decimalator]

RAIS, our IIIF server, caches images from S3 onto disk, and may optionally be caching image tiles in memory. When things change in Oregon Digital, we're going to want to make sure these caches get cleared so old images aren't showing up in the views.

[jechols]

See uoregon-libraries/rais-image-server#15 - this is in progress and should be ready soon. (It's code-complete but still needs a little bit of testing)

[jechols]

Testing this can be done manually by standing up RAIS, but the real test is making it work within our stack. Scenarios I see:

• An image is deleted
  • Ingest an image
  • View it with RAIS (i.e., verify that it's been processed for universal viewer)
  • Delete the image in OD
  • Verify that RAIS purged the image from its cache - this may require a low-level filesystem check
• An image is modified
  • Ingest an image
  • View it with RAIS (i.e., verify that it's been processed for universal viewer)
  • Modify the image in OD
  • Verify that RAIS purged the image from its cache - this may require a low-level filesystem check
  • Verify that viewing the new asset in universal viewer doesn't have remnants of the old image
• A PDF is deleted
  • Ingest a PDF
  • View all pages with RAIS
  • Delete the PDF in OD
  • Verify that RAIS purged all pages' images from its cache - this may require a low-level filesystem check
• A PDF is modified
  • Ingest a PDF
  • View all pages with RAIS
  • Update the PDF in OD
  • Verify that RAIS purged all pages' images from its cache - this may require a low-level filesystem check
  • Verify that all pages are for the new PDF; no remnants of the old cache show up
• An asset's metadata is changed, but the image or pdf don't change
  • Ingest an asset (image or PDF)
  • View it with RAIS
  • Update the asset's metadata without changing its image
  • Verify RAIS still has the image cached
  • This scenario may not be a huge priority; worst-case scenario is purging more from our cache than we technically need to

[vantuyls]

@jechols @decimalator so, without a description on this issue, it is not clear to me what the issue is for. clarification please

[jechols]

Closing this issue. Testing of RAIS wouldn't make sense in OD-land, so what we need is a new ticket for getting the purge calls in. That ticket would be the one we'd test.