Add new model: GeoLM
# What does this PR do?

Add a new model called **GeoLM** into the Transformer library. GeoLM is a language model based on BERT that facilitates **geospatial understanding** in NL documents. It is pretrained on world-wide OpenStreetMap (OSM), WikiData and Wikipedia data, and can be adapted to various geospatial related downstream tasks such as **toponym recognition** and **toponym linking**. 

## Model Weights:
* Pretrained GeoLM (ready-to-use for zero-shot toponym linking): [zekun-li/geolm-base-cased](https://huggingface.co/zekun-li/geolm-base-cased)
* Fine-tuned GeoLM for toponym recognition: [zekun-li/geolm-base-toponym-recognition](https://huggingface.co/zekun-li/geolm-base-toponym-recognition)

## Open source status

- [x]  The model implementation is available in this PR
- [x]  The model weights are available in HuggingFace model hub

<!--
Congratulations! You've made it this far! You're not quite done yet though.

Once merged, your PR is going to appear in the release notes with the title you set, so make sure it's a great title that fully reflects the extent of your awesome contribution.

Then, please replace this with a description of the change and which issue is fixed (if applicable). Please also include relevant motivation and context. List any dependencies (if any) that are required for this change.

Once you're done, someone will review your PR shortly (see the section "Who can review?" below to tag some potential reviewers). They may suggest changes to make the code even better. If no one reviewed your PR after a week has passed, don't hesitate to post a new comment @-mentioning the same persons---sometimes notifications get lost.
-->


## Who can review?

Anyone in the community is free to review the PR once the tests have passed. 

Feel free to tag members/contributors who may be interested in your PR: @ArthurZucker and @younesbelkada

<!-- Your PR will be replied to more quickly if you can figure out the right person to tag with @

 If you know how to use git blame, that is the easiest way, otherwise, here is a rough guide of **who to tag**.
 Please tag fewer than 3 people.

Models:

- text models: @ArthurZucker and @younesbelkada
- vision models: @amyeroberts
- speech models: @sanchit-gandhi
- graph models: @clefourrier

Library:

- flax: @sanchit-gandhi
- generate: @gante
- pipelines: @Narsil
- tensorflow: @gante and @Rocketknight1
- tokenizers: @ArthurZucker
- trainer: @sgugger

Integrations:

- deepspeed: HF Trainer/Accelerate: @pacman100
- ray/raytune: @richardliaw, @amogkam

Documentation: @sgugger, @stevhliu and @MKhalusova

HF projects:

- accelerate: [different repo](https://github.com/huggingface/accelerate)
- datasets: [different repo](https://github.com/huggingface/datasets)
- diffusers: [different repo](https://github.com/huggingface/diffusers)
- rust tokenizers: [different repo](https://github.com/huggingface/tokenizers)

Maintained examples (not research project or legacy):

- Flax: @sanchit-gandhi
- PyTorch: @sgugger
- TensorFlow: @Rocketknight1

 -->

This PR contains redundant commits and failed test cases. I will fix them and create a new PR later. 