Fail more descriptively when time is not found

[j08lue]

A request like

https://dev-titiler-cmr.delta-backend.com/tiles/WebMercatorQuad/0/0/0@1x?datetime=2024-10-20T22%3A00%3A00.000Z&resampling=bilinear&variable=precipitation&colormap_name=gnbu&rescale=0%2C46&concept_id=C2723754864-GES_DISC&backend=xarray

where the dataset only has time steps until say 2022-01-01

currently fails with a 500 error and

{"detail":"list index out of range"}

Error code and message could be more descriptive when the requested datetime is not found.

[abarciauskas-bgse]

Thank you for opening this @j08lue - I'm going to move it to titiler-cmr