[Feature] Add another mode for the tag cache

[conico974]

Right now the tag cache is made to work mostly with DynamoDB and does not work in the same way as in next standalone. We should add a different mode for the tag cache (and support both) that would work in the same way as in next standalone.

We should probably add a dynamodb-nextmode override and add some docs explaining the difference and which one you should choose

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Current Implementation

On get

We just check for the cache key in the tag cache. If it has been revalidated we just return null, otherwise we continue

On set

We have to write both the incremental cache and check the tag cache for non existing tag/key combination. For non existing tag/key combination, we have to add them

On revalidateTag for each tag

We have to update every possible combination for the requested tag

Pros

• Very fast on read
• Only one query per get (On DynamoDB it's a lot cheaper)
• Can allow for automatic cdn invalidation on revalidateTag

Cons

• Lots of write on set and revalidateTag
• Needs to be prepopulated at build time to work properly

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New Mode

On get

We have to check for every tag (after reading the incremental cache) that they have not been revalidated.

In DynamoDB, this would require 1 GetItem per tag (including internal one), more realistically 1 BatchGetItem per get (In terms of pricing, it would be billed as multiple single GetItem)

On set

We don't have to do anything here

On revalidateTag for each tag

We have to update a single entry for this tag

Pros

• No need to prepopulate DDB
• Very little write

Cons

• Might be slower on read
• One page request (i.e. GET request) could require to check a lot of tags (And some of them multiple time when used with the fetch cache)
• Almost impossible to do automatic cdn revalidation by itself