dir-index-html: add indicator if CID is cached in local datastore

Is your feature request related to a problem? Please describe.

As a user of IPFS, it's difficult to visualize if files are cached on the gateway you're connected to vs if the files need to be retrieved from the network.

Describe the solution you'd like An indicator to show if a CID is cached on the current gateway.

Example (horrible) mock up:

The first three entries are cached on the gateway, the final one would require pulling from other IPFS nodes. Three indicators may be needed:

• Fully cached locally
• Partially cached locally
• Not cached locally