(fix):Pass full context to S3 context handler (#2221)

On version 1.9.0 context fetch from S3 is broken since `url.Parse` requires full path: https://github.com/GoogleContainerTools/kaniko/blob/90e426ba3fde4b72efbcec5f10e4f73963313228/pkg/util/bucket/bucket_util.go#L77
Currently on a --context=s3://my-bucket/my-path/context.tar.gz we would pass only my-bucket/my-path/context.tar.gz which breaks context fetch

Closes #2200

pkg/buildcontext/buildcontext.go

@@ -50,9 +50,9 @@ func GetBuildContext(srcContext string, opts BuildOptions) (BuildContext, error)
 
 		switch prefix {
 		case constants.GCSBuildContextPrefix:
-			return &GCS{context: context}, nil
+			return &GCS{context: srcContext}, nil
 		case constants.S3BuildContextPrefix:
-			return &S3{context: context}, nil
+			return &S3{context: srcContext}, nil
 		case constants.LocalDirBuildContextPrefix:
 			return &Dir{context: context}, nil
 		case constants.GitBuildContextPrefix: