Add uption to create (POST) metadata in update_metadata function in the resource class

This MR fixes the update_metadata function in the fact that there is no way to create metadata for existing file objects in Coscine that do not have metadata assigned yet (e.g. in RDS-S3 resources). The function doc string did state it handles this, but this was not the case.

Furthermore, I have also included an option to overwrite files or not in the upload function (may have been smart to do this in another MR... I could revert and split things, let me know).

src/coscine/resource.py

@@ -570,7 +570,8 @@ class Resource:
         path: str,
         handle: BinaryIO | bytes | str,
         metadata: MetadataForm | dict | rdflib.Graph | None = None,
-        progress: Callable[[int], None] | None = None
+        progress: Callable[[int], None] | None = None,
+        overwrite: bool =True
     ) -> None:
         """
         Uploads a file-like object to a resource in Coscine.
@@ -590,6 +591,9 @@ class Resource:
         progress
             Optional callback function that gets occasionally called
             during the upload with the progress in bytes.
+        overwrite
+            Bool that designates whether existing files should be overwritten.
+            Default set to True (files will be overwritten).
         """
         if isinstance(metadata, MetadataForm):
             metadata = metadata.serialize(path)
@@ -615,12 +619,20 @@ class Resource:
         if isinstance(handle, bytes):
             handle = BytesIO(handle)
         if metadata is not None:
-            self.post_metadata(metadata)
-        assert isinstance(handle, IOBase)
-        if self.type.general_type == "rdss3":
-            self._upload_blob_s3(path, handle)
+            try:
+                self.post_metadata(metadata)
+            except RequestRejected:
+                self.put_metadata(metadata)
+        assert isinstance(handle, IOBase) 
+
+        if overwrite or path not in [f.name for f in self.files()]:
+            if self.type.general_type == "rdss3":
+                self._upload_blob_s3(path, handle)
+            else:
+                self._upload_blob(path, handle, progress)
         else:
-            self._upload_blob(path, handle, progress)
+            print('File already exists and overwrite is set to False!')
+        
 
     def post_metadata(self, metadata: dict) -> None:
         """
@@ -656,7 +668,12 @@ class Resource:
         This comes at the cost of possibly sending two requests, where
         one would have sufficed.
         """
-        self.put_metadata(metadata)
+        try:
+            self.put_metadata(metadata)
+        except RequestRejected:
+            self.post_metadata(metadata)
+
+        
 
     def _upload_blob(
         self,