Add support for named dimensions and coordinates like in xarray

[twiecki]

This came up in a conversation with @aseyboldt.

In PyMC3 the dims feature that allows naming of shapes leads to great UX. It would be great to push this down into Aesara and extend it. One thing that would be nice is to have named indices so that one could do:
x["foo"] instead of x[0].

Same with dimensions: x.sum(axis="bar"). A lot could probably be borrowed from xarray who are doing this really well.

[lucianopaz]

Just to link this, as it could be useful, Torch does something like this with named tensors. Numpy also has its structured arrays, but those are much more flexible than what we need to get names into dimensions.

I think that the key thing that we would need to do as a bare minimum is to handle dimension name propagation through the graph.

[OriolAbril]

This might be useful to follow and see if making xarray use Aesara as computational backend can male thia possible without extra work on Aesara

[jhamman]

Cross linking a discussion I just started in the Xarray repo on this subject: pydata/xarray#7515

[brandonwillard]

Cross linking a discussion I just started in the Xarray repo on this subject: pydata/xarray#7515

Thanks!