V15: Cache Seeding

[nikolajlauridsen]

Implement cache seeding for Document and Media cache, enable seeded content to remain pinned, and fix various issues and todos.

Documents and media can both be seeded with a breadth-first search, there's been added new app settings for both to specify how many nodes should be seeded.

For documents, you can also seed a document type basis.

I found a couple of issues as well when working on this:

• IIdKeyMap is used too much, for instance when deleting, I've fixed this by implementing GetContentSourceAsync with key instead of only id.
• Found an issue in ToContentCacheNode where the templates were switched, so the published template was returned for unpublished content and vice versa.
• Found a weird one, where because we cache published and draft separately RefreshContentAsync was called twice, once for the published, and once for draft, but RefreshContentAsync refreshed both regardless, I've added a check on IsDraft here

Testing

Test that the expected nodes are seeded, either by setting a breakpoint in the seed methods, or ideally by setting up a level two cache as specified in #16938, this will then allow you to look in the created DB table to see if the expected ids are cached.

It's also possible to set a breakpoint in GetContentSourceAsync in the DatabaseCacheRepository and ensure that this is not hit when resolving the seeded items.