Draft release notes to ease with upgrade from 6 to 7

[mjgiarlo]

For now, use this issue to list steps that may be needed for the upgrade to 7.0.0

• Make sure that new config option(s?) are generated into existing initializers, e.g.:
  • https://github.com/projecthydra/sufia/pull/1747#discussion_r58423355
  • https://github.com/projecthydra/sufia/pull/1799
  • https://github.com/projecthydra/sufia/pull/2028/files#diff-70cc36be61e57f96ec44887d4d62aa0f
  • https://github.com/projecthydra/sufia/pull/2096/files#diff-70cc36be61e57f96ec44887d4d62aa0f
  • https://github.com/projecthydra/sufia/pull/2217/files#diff-70cc36be61e57f96ec44887d4d62aa0f
  • https://github.com/projecthydra/sufia/pull/2406/files#diff-70cc36be61e57f96ec44887d4d62aa0f
• Steps related to data migration (refs #997)
• Move UploadSet into the local application if you care about retaining "related files"-like functionality (from Sufia 6) for Works in Sufia 7.
• Sufia no longer provides a catch-all 404 route. Folks may want to add something similar to their apps. Refs #1906
• CurationConcerns and Sufia no longer support Resque; they both use ActiveJob. It's up to applications to decide what queuing back-end they want to use. Folks coming from Sufia 6 will have Resque/-pool relics in their codebases, though, and we should verify those continue to work and if they don't, provide some documentation or tooling to help bring them along.
• Rights are now handled differently: https://github.com/projecthydra-labs/curation_concerns/commit/2e60b6d954c60cf25236ad22f31177f18d33a54d
• Hydra ACLs are now aligned with F4. They'll need to be migrated. See the HH release notes: https://github.com/projecthydra/hydra-head/releases/tag/untagged-25364fefde9999139f5b (currently untagged but will be the 10.0.0 release)
• Do s/tag/keyword/ in your app's app/controllers/catalog_controller.rb
• Changed views to know about in case they've been overridden downstream
  • lots and lots of them, like https://github.com/projecthydra/sufia/pull/2028/files
• Remove config/initializers/stats_admin.rb (https://github.com/projecthydra/sufia/pull/2192/files#diff-b16625ebe7ae114b4f5d1415b40091c1)
• Use ConnectedWithModel in SolrDocumentBehavior
• ...

[mjgiarlo]

Related to #997. THIS ticket is more about the software upgrade.

[mjgiarlo]

Preliminary work on this is reflected here: https://github.com/psu-stewardship/scholarsphere/wiki/Migration-to-PCDM

[mjgiarlo]

@hackmastera @cam156 @pgwillia Do y'all have anything to add to this ticket, about upgrading Sufia from 6 to 7? (Re: the upgrade itself, not data migration.) I'm wondering whether this should block 7.3.0 or not, and if so, who might have capacity to help.