fix: enforce 5gb copy source object size threshold.

Fixes #1896

Enforces the S3 `5 GiB` copy source size limit across the posix and azure
backends for `CopyObject` and `UploadPartCopy`, returning `InvalidRequest` when
the source object exceeds the threshold.

The limit is now configurable via `--copy-object-threshold`
(`VGW_COPY_OBJECT_THRESHOLD`, default 5 GiB).
A new `--mp-max-parts flag` (`VGW_MP_MAX_PARTS`, default `10000`) has been added to make multipart upload parts number limit configurable.

No integration test has been added, as GitHub Actions cannot reliably
handle large objects.

s3api/controllers/base.go

@@ -38,6 +38,7 @@ type S3ApiController struct {
 	logger        s3log.AuditLogger
 	evSender      s3event.S3EventSender
 	mm            metrics.Manager
+	mpMaxParts    int
 	readonly      bool
 	disableACL    bool
 	virtualDomain string
@@ -60,7 +61,7 @@ var (
 	xmlhdr = []byte(`<?xml version="1.0" encoding="UTF-8"?>` + "\n")
 )
 
-func New(be backend.Backend, iam auth.IAMService, logger s3log.AuditLogger, evs s3event.S3EventSender, mm metrics.Manager, readonly, disableACL bool, virtualDomain string) S3ApiController {
+func New(be backend.Backend, iam auth.IAMService, logger s3log.AuditLogger, evs s3event.S3EventSender, mm metrics.Manager, readonly, disableACL bool, virtualDomain string, mpMaxParts int) S3ApiController {
 	return S3ApiController{
 		be:            be,
 		iam:           iam,
@@ -70,6 +71,7 @@ func New(be backend.Backend, iam auth.IAMService, logger s3log.AuditLogger, evs
 		mm:            mm,
 		disableACL:    disableACL,
 		virtualDomain: virtualDomain,
+		mpMaxParts:    mpMaxParts,
 	}
 }