Render mesh annotations in neuroglancer

[manasaV3]

Add support to render mesh annotations as multiscale mesh in neuroglancer using https://github.com/chanzuckerberg/cryoet-data-portal-neuroglancer.

Tasks involved

• Add precompute handler for the mesh annotation.
• Update neuroglancer config to add mesh layer

[manasaV3]

Blocked by dependency on functionality implementation in https://github.com/chanzuckerberg/cryoet-data-portal-neuroglancer