Xarray-sentinel

Added `incidence_angle_mid_swath` metadata and `mosaic_slc_iw` helper function, needed by Sarsen.

Allow accessing GRD in the Planetary computer by passing `override_product_files="{dirname}/{prefix}{swath}-{polarization}{ext}"`.

**What's new:**
- Fixed chunking of measurement data
- Added a helper functions for simple operations involving metadata
- Start adding metadata to variables

**Overview:**

Overall the software is in the **alpha** phase and the usual caveats apply.

- supports the following data products as [distributed by ESA](https://scihub.copernicus.eu/dhus/#/home):
- Sentinel-1 Ground Range Detected (GRD):
- Stripmap (SM)
- Interferometric Wide Swath (IW)
- Extra Wide Swath (EW)
- Sentinel-1 Single Look Complex (SLC) SM/IW/EW
- creates ready-to-use [Xarray](https://xarray.pydata.org) `Dataset`s that map the data lazily and efficiently in terms of both memory usage and disk / network access
- reads all SAR imagery data: GRD images, SLC swaths and SLC bursts
- reads several metadata elements: satellite orbit and attitude, ground control points, radiometric calibration look up tables, Doppler centroid estimation and more
- reads uncompressed and compressed SAFE data products on the local computer or on a network via [*fsspec*](https://filesystem-spec.readthedocs.io) - **depends on rasterio>=1.3a3**
- supports larger-than-memory and distributed data access via [*Dask*](https://dask.org) and [*rioxarray*](https://corteva.github.io/rioxarray) / [*rasterio*](https://rasterio.readthedocs.io) / [*GDAL*](https://gdal.org)
- provides a few helpers for simple operations involving metadata like croppping individual bursts out of IW SLC swaths applying radiometric calibration polynomials and converting slant to ground range for GRD products

Overall the software is in the **alpha** phase and the usual caveats apply.

- supports the following data products as [distributed by ESA](https://scihub.copernicus.eu/dhus/#/home):
- Sentinel-1 Ground Range Detected (GRD): **NEW**
- Stripmap (SM)
- Interferometric Wide Swath (IW)
- Extra Wide Swath (EW)
- Sentinel-1 Single Look Complex (SLC) SM/IW/EW
- creates ready-to-use [Xarray](https://xarray.pydata.org) `Dataset`s that map the data lazily and efficiently in terms of both memory usage and disk / network access
- reads all SAR imagery data: GRD images, SLC swaths and SLC bursts
- reads several metadata elements: satellite orbit and attitude, ground control points, radiometric calibration look up tables, Doppler centroid estimation and more
- reads uncompressed and compressed SAFE data products on the local computer or
on a network via [*fsspec*](https://filesystem-spec.readthedocs.io) - **depends on rasterio>=1.3a3**
- supports larger-than-memory and distributed data access via [*Dask*](https://dask.org) and [*rioxarray*](https://corteva.github.io/rioxarray) / [*rasterio*](https://rasterio.readthedocs.io) / [*GDAL*](https://gdal.org)

Fix the crash on products generated by the new IPF 3.40 processor 79

Overall the software is in the **alpha** phase and the usual caveats apply.
A few features, identified as *technology preview* below, are not fully usable yet.

- supports the following data products as [distributed by ESA](https://scihub.copernicus.eu/dhus/#/home):
- Sentinel-1 Single Look Complex (SLC):
- Stripmap (SM)
- Interferometric Wide Swath (IW)
- Extra Wide Swath (EW)
- Wave (WV) - *technology preview*
- Sentinel-1 Ground Range Detected (GRD) SM/IW/EW/WV - *technology preview*
- creates ready-to-use [Xarray](https://xarray.pydata.org) `Dataset`s that map the data
lazily and efficiently in terms of both memory usage and disk / network access
- reads all SAR imagery data: GRD images, SLC swaths and SLC bursts
- reads several metadata elements:
satellite orbit and attitude, ground control points, radiometric calibration look up tables,
Doppler centroid estimation and more
- reads uncompressed and compressed SAFE data products on the local computer or
on a network via [*fsspec*](https://filesystem-spec.readthedocs.io) - *technology preview*
- allows larger-than-memory and distributed processing via [*dask*](https://dask.org)