Support for instance remove from collection folder

[JOJ0]

@captain-cronch discovered that the remove_release() method we have

https://github.com/joalla/discogs_client/blob/b73595dbf1c4f4677401b5062486613a0c8a08ad/discogs_client/models.py#L760:764

is misleading - it removes from the collection entirely instead of only from a collection folder.

Further investigation reveals that the provided endpoint of the Discogs API is slightly confusing already, but after reading carefully it's somewhat documented:

https://www.discogs.com/developers#page:user-collection,header:user-collection-delete-instance-from-folder

Currently python3-discogs-client supports sending a DELETE request but not a POST request to that endpoint.

Find below, the original message including a well done implementation suggestion already.

I'd like to open discussion of that suggestion and ask for further ideas especially on how the method should be named and how we should document it.

Original post (slightly edited)

I used the following using requests to accomplish what I was after:

url = f"https://api.discogs.com/users/{username}/collection/folders/{folder_id}/releases/{release_id}/instances/{instance_id}"

data = {'folder_id': target_folder_id}

response = requests.post(url, auth=auth, json=data)

I looked through models.py and believe there's not currently a function that accomplishes this (perhaps I'm not passing optional arguments somewhere though). In the class CollectionFolder, a function called move_release would be useful and probably look something like this:

def move_release(self, instance, target_folder_id):
    if not isinstance(instance, CollectionItemInstance):
        raise TypeError('instance must be of type CollectionItemInstance')
    instance_url = self.fetch('resource_url') + '/releases/{0}/instances/{1}'.format(instance.id, instance.instance_id)
    data = {'folder_id': target_folder_id}
    self.client._post(instance_url, data)

As mentioned earlier, I wanted to remove a release from a folder, but to accomplish that it must be moved to a different folder (such as the uncategorized folder). This function also allows the passing of a different target_folder_id and would result in an existing instance being moved from its current folder to the target folder.

Originally posted by @captain-cronch in #160 (reply in thread)

[JOJ0]

@captain-cronch I'd like to encourage you, since your suggestion seems pretty good to me already, to open a draft PR and we work from there? That would help us a lot! We certainly will assist with setting up a dev environment, answer questions, and so on.