Add option to avoid loading duplicate indexes across many datasets

[danielfromearth]

When using earthaccess.open_virtual_mfdataset() to concatenate many granules that share the same indexes (for example, with NASA Level 3 data), it seems that the same information is being downloaded many times.

This came up in a discussion during the earthaccess hackday on 15 April 2025, with @battistowx, @betolink, @Mikejmnez
Would love to hear your thoughts on this too, @ayushnag!

[battistowx]

Using xarray.align with join='override' might be part of the workflow to fix this: https://docs.xarray.dev/en/latest/generated/xarray.align.html