New Ifremer STAC backend for ArgoIndex

STAC stands for SpatioTemporal Asset Catalogs

> The STAC specification is a common language to describe geospatial information, so it can more easily be worked with, indexed, and discovered.

Ifremer is implementing a STAC catalog for Argo floats and profiles: https://stac-browser.ifremer.fr/

It would be "very" FAIR to provide such a STAC backend for the [argopy ArgoIndex class](https://argopy.readthedocs.io/en/latest/advanced-tools/stores/argoindex.html).

In practice, this would means that the ArgoIndex will rely on STAC http requests, rather than index file.

**The strong added value of this feature would be an ArgoIndex that would not need to load an index file in memory**.

But it remains to be determined how this could fit with the current design of ArgoIndex, which has already 2 backends to handle index csv content, as Pandas Dataframe or Pyarrow Tables.

It could go like this:

```python
from argopy import ArgoIndex
idx = ArgoIndex(host='stac')
```

Also I don't know yet:
- how to search the catalog of floats or profiles ([from the api](https://stac-pg-api.ifremer.fr/search) called by the [stac-browser](https://stac-browser.ifremer.fr/search)),
- if this would necessarily need the [pystac library](https://pystac.readthedocs.io/en/stable/index.html) (see also [xpystac](https://github.com/stac-utils/xpystac/tree/main)).

poke @tcarval