feat: add response header overrides for GetObject

GetObject allows overriding response headers with the following
paramters:
response-cache-control
response-content-disposition
response-content-encoding
response-content-language
response-content-type
response-expires

This is only valid for signed (and pre-singed) requests. An error
is returned for anonymous requests if these are set.

More info on the GetObject overrides can be found in the GetObject
API reference.

This also clarifies the naming of the AccessOptions IsPublicBucket
to IsPublicRequest to indicate this is a public access request
and not just accessing a bucket that allows public access.

Fixes #1501

s3api/utils/utils.go

@@ -779,3 +779,20 @@ func ValidateCopySource(copysource string) error {
 
 	return nil
 }
+
+// GetQueryParam returns a pointer to the query parameter value if it exists
+func GetQueryParam(ctx *fiber.Ctx, key string) *string {
+	value := ctx.Query(key)
+	if value == "" {
+		return nil
+	}
+	return &value
+}
+
+// ApplyOverride returns the override value if it exists and status is 200, otherwise returns original
+func ApplyOverride(original, override *string) *string {
+	if override != nil {
+		return override
+	}
+	return original
+}