V15: Add custom serializer for hybrid cache (#17727)

* Add custom serializer

* Add migration to rebuild cache

* Rename migration namespace to 15.1

* Also clear media cache

* Remove failed cache items

* Refactor to only use keys for document cache repository

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Co-authored-by: nikolajlauridsen <nikolajlauridsen@protonmail.ch>

src/Umbraco.PublishedCache.HybridCache/ContentCacheNode.cs

@@ -4,7 +4,7 @@ namespace Umbraco.Cms.Infrastructure.HybridCache;
 
 // This is for cache performance reasons, see https://learn.microsoft.com/en-us/aspnet/core/performance/caching/hybrid?view=aspnetcore-9.0#reuse-objects
 [ImmutableObject(true)]
-internal sealed class ContentCacheNode
+public sealed class ContentCacheNode
 {
     public int Id { get; set; }