Add support for loading adapters from HuggingFace Model Hub

[calpt]

WIP for adding HuggingFace's model hub as a second source for loading adapters. Implementation via https://github.com/huggingface/huggingface_hub.

Example

Adapter: https://huggingface.co/calpt/adapter-bert-base-squad1

Loading from HF Hub

model = BertForSequenceClassification.from_pretrained("bert-base-uncased")
model.load_adapter("calpt/adapter-bert-base-squad1", source="hf")

Loading (the same adapter) from AdapterHub

model = BertForSequenceClassification.from_pretrained("bert-base-uncased")
model.load_adapter("squad1", config="houlsby", source="ah")  # source="ah" is default & can be omitted

[osanseviero]

Hi @calpt!

This PR looks awesome 🔥 thank you! I'll follow-up with some things from our side. What do you think of having a code snippet and a tag so people can search for all adapters in the 🤗 Hub?

This is an example of a code snippet that we could have. Let me know what you think

from transformers import AutoModelWithHeads

model = AutoModelWithHeads.from_pretrained("{model inferred from model_name in adapter_config.json}")
model.load_adapter("model name", source="hf")

Thanks once more!

[calpt]

Hi @osanseviero!

Looks great! Thanks for looking into this and let me know if you need anything else from our side.

[osanseviero]

Hey Calpt! Nothing else from your side at the moment until this PR is submitted. We're adding code snippets for adapter transformers which reads from adapter_config.json as discussed 🚀 🌔 . Feel free to take a look:

huggingface/huggingface_hub#62

[osanseviero]

From the Hub side, if you add - adapter-transformers to the tags, you get a working code snippet that uses adapter_config.json. Check out https://huggingface.co/calpt/adapter-bert-base-squad1 for example.

[calpt]

@osanseviero Looks great! Thanks so much for your support on this! We'll add some documentation on our side and release this with the next feature update.