Remove errors.Cause() usage from cardinality analysis handler

[pracucci]

What this PR does

In this PR I'm removing errors.Cause() from respondFromError(), which is only used by the cardinality analysis handler. The errors.Cause() was passed to httpgrpc.HTTPResponseFromError() which, in turn, passes the error to grpcutil.ErrorToStatus(). grpcutil.ErrorToStatus() (see code) uses errors.As() (which navigates the chain of wrapped errors), so the errors.Cause() usage should be superfluous.

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.

[narqo]

🔥 looks good, overall

(nit) It seems that the import of pkg/errors in this file, can now be replaced with stdlib's error, right?

[pracucci]

(nit) It seems that the import of pkg/errors in this file, can now be replaced with stdlib's error, right?

I think it can, but it's unrelated from work. This work is about not using errors.Cause() because it's incompatible with standard errors package, while we haven't took any decision whether we want to uniform towards standard errors package or not (currently we use a mix of the two in Mimir).