add metadata about spatial index

[wiesehahn]

I think it might make sense to add information whether a pointcloud has a spatial index.

E.g. LASfiles can have an external .lax file file or the index can be integrated in laz files. I would propose a boolean attribute, something like
"pc:indexed": true

what do you think?

[gadomski]

• For an external file index, the lax file could just be another asset on the item?
• For the internal index, does a boolean flag help a client at all? E.g. can a client make some sort of assumption about how it accesses the file? Or does a client still need to read the file's metadata to learn where the index lives in the blob?