refactor(s3): Move all cache files to the cache/ folder

[ViBiOh]

What does this PR do?

Change the location of caches files under a cache/ folder prefix. So that it's allowed by the Policy and will result in a NotFoundException instead of AccessDeniedException, as explained here.

Motivation

avoid CloudTrail pollution for AccessDeniedException

Testing Guidelines

Additional Notes

Types of changes

• Bug fix
• New feature
• Breaking change
• Misc (docs, refactoring, dependency upgrade, etc.)

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[klivan]

My concern is that List* operations are 10x more expensive than Get*, so we'll 10x customers' costs for these checks.

[tyrcho]

My concern is that List* operations are 10x more expensive than Get*, so we'll 10x customers' costs for these checks.

If this cost becomes a concern, I guess we could offer both alternatives, configurable with an env variable.
By default we should keep the existing behaviour, and if the variable is set we would switch to List operations to reduce CloudTrail pollution with some extra S3 cost.