/active_series: generate correct request shards for incoming GET requests, handle gRPC errors

[flxbk]

What this PR does

This PR addresses two issues I discovered while testing the active series API.

• Shard requests generated for incoming active series requests with method GET and a selector parameter in the query string were broken and did not include the modified shard selector. Therefore, the results would always contain the set of series duplicated as many times as there are request shards.
• Handling context.Canceled is not sufficient for grpc related calls, we also need to handle status.Code(err) == codes.Canceled. Following up on a review comment, I have moved and reused code from pkg/storegateway which already solves this issue.

Which issue(s) this PR fixes or relates to

Fixes #

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.

[colega]

It would be nice to reuse this piece of code:

mimir/pkg/storegateway/storegatewaypb/custom.go

Lines 105 to 162 in c39af79

	func wrapContextError(err error) error {
	if err == nil {
	return nil
	}
	// Get the gRPC status from the error.
	type grpcErrorStatus interface{ GRPCStatus() *grpcstatus.Status }
	var grpcError grpcErrorStatus
	if !errors.As(err, &grpcError) {
	return err
	}
	switch status := grpcError.GRPCStatus(); {
	case status.Code() == codes.Canceled:
	return &grpcContextError{grpcErr: err, grpcStatus: status, stdErr: context.Canceled}
	case status.Code() == codes.DeadlineExceeded:
	return &grpcContextError{grpcErr: err, grpcStatus: status, stdErr: context.DeadlineExceeded}
	default:
	return err
	}
	}
	// grpcContextError is a custom error used to wrap gRPC errors which maps to golang standard context errors.
	type grpcContextError struct {
	// grpcErr is the gRPC error wrapped by grpcContextError.
	grpcErr error
	// grpcStatus is the gRPC status associated with the gRPC error. It's guaranteed to be non-nil.
	grpcStatus *grpcstatus.Status
	// stdErr is the equivalent golang standard context error.
	stdErr error
	}
	func (e *grpcContextError) Error() string {
	return e.grpcErr.Error()
	}
	func (e *grpcContextError) Unwrap() error {
	return e.grpcErr
	}
	func (e *grpcContextError) Is(err error) bool {
	return errors.Is(e.stdErr, err) || errors.Is(e.grpcErr, err)
	}
	func (e *grpcContextError) As(target any) bool {
	if errors.As(e.stdErr, target) {
	return true
	}
	return errors.As(e.grpcErr, target)
	}
	func (e *grpcContextError) GRPCStatus() *grpcstatus.Status {
	return e.grpcStatus
	}

So the check would be just:

if errors.Is(coolgrpc.WrapContextError, context.Canceled)

cc @pracucci who wrote that code in case he wants to express an opinion on reusing it.

[flxbk]

I have moved this code to util and reused it in this PR. Happy to have your suggestions in case you think we can improve naming and/or the location of this code (should it be a separate package?).