Expand cache examples

Problem/Motivation

Cache examples needs more things:

• Demo renderable cache metadata:
• max-age
• tags
• keys
• contexts
• Demo implementing a cache context.
• Demonstrate allowing invalid cache items.
• Demonstrate deleting cache entries.
• Demonstrate deleting cache tags.
• Demonstrate deleting all cache items.
• Demonstrate invalidating cache entries.
• Demonstrate invalidating cache tags.
• Demonstrate invalidating all cache items.

Proposed resolution

Pick an item. Add a child issue for it.

Remaining tasks

User interface changes

API changes

Data model changes