Simple S3 client (#836)

This functionality is intended to be used to manage datasets for test cases, but may be useful elsewhere in the future.

- **Add S3 client with AWS Signature V4 (SigV4) signing** — new `S3Client` in `zenutil/cloud/` supporting `GetObject`, `PutObject`, `DeleteObject`, `HeadObject`, and `ListObjects` operations
- **Add EC2 IMDS credential provider** — automatically fetches and refreshes temporary AWS credentials from the EC2 Instance Metadata Service (IMDSv2) for use by the S3 client
- **Add SigV4 signing library** — standalone implementation of AWS Signature Version 4 request signing (headers and query-string presigning)
- **Add path-style addressing support** — enables compatibility with S3-compatible stores like MinIO (in addition to virtual-hosted style)
- **Add S3 integration tests** — includes a `MinioProcess` test helper that spins up a local MinIO server, plus integration tests exercising the S3 client end-to-end
- **Add S3-backed `HttpObjectStoreService` tests** — integration tests verifying the zenserver object store works against an S3 backend
- **Refactor mock IMDS into `zenutil/cloud/`** — moved and generalized the mock IMDS server from `zencompute` so it can be reused by both compute and S3 credential tests

1 files changed, 6 insertions, 0 deletions

diff --git a/src/zenutil/zenutil.cpp b/src/zenutil/zenutil.cpp
index 291dbeadd..734813b69 100644
--- a/src/zenutil/zenutil.cpp
+++ b/src/zenutil/zenutil.cpp
@@ -4,6 +4,9 @@
 
 #if ZEN_WITH_TESTS
 
+#	include <zenutil/cloud/imdscredentials.h>
+#	include <zenutil/cloud/s3client.h>
+#	include <zenutil/cloud/sigv4.h>
 #	include <zenutil/rpcrecording.h>
 #	include <zenutil/config/commandlineoptions.h>
 #	include <zenutil/wildcard.h>
@@ -15,6 +18,9 @@ zenutil_forcelinktests()
 {
 	cache::rpcrecord_forcelink();
 	commandlineoptions_forcelink();
+	imdscredentials_forcelink();
+	s3client_forcelink();
+	sigv4_forcelink();
 	wildcard_forcelink();
 }