Add Sentinel-3 Multi-Product Demo notebook

[Yuvraj198920]

Migrate comprehensive Sentinel-3 multi-product demo notebook from GDAL-ZARR-EOPF repository. Covers OLCI L1/L2 and SLSTR L1/L2 products using GDAL EOPFZARR driver.

[tinaok]

Hi, do you have same problem I reported here?
https://gitlab.eopf.copernicus.eu/cpm/eopf-cpm/-/issues/995

[Yuvraj198920]

Hi @tinaok, thanks for the reference! Our notebook uses the GDAL EOPFZARR driver directly (not xarray), so we don't encounter the same dimension alignment issue with /quality/orphans. We read individual bands by path, which bypasses the xarray alignment step where the inconsistent dim_0/dim_1 vs rows/removed_pixels names cause problems. Good to know the fix is coming in 2.6.5!