Chore: remove superfluous errors.Cause() usage in pkg/storage

[pracucci]

What this PR does

In this PR I'm removing superfluous errors.Cause() usage in pkg/storage. This usage of errors.Is(errors.Cause(), ...) was introduced in #3288 when removing Thanos dependency.

The reason why errors.Cause() is superfluous is because errors.Is() already navigates the chain of wrapped errors, so we don't have to look at the Cause() of an error. I've checked all places where these errors are returned, and they're all correctly wrapped with errors.Wrap() (so errors.Is() is enough). In addition, for the errors returned by ReadMarker(), in other places in the code we just check the same errors using only errors.Is(), another signal that errors.Cause() is not needed.

Note: this PR is part of a work I'm doing to completely remove errors.Cause() from Mimir.

Which issue(s) this PR fixes or relates to

N/A

Checklist

• Tests updated.
• Documentation added.
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX].
• about-versioning.md updated with experimental features.