Additional AMS datasets

[jpswinski]

Implement AMS for ATL03, ATL06, ATL08; with enhanced metadata query support (per granule and as a part of the query parameters that filter out which granules are returned). Also need a way to version AMS databases (and report the version in the response) to support multiple releases of the standard data products.

[jpswinski]

For consideration:

• Use h5coro to traverse a granule supplied to the request and report back a definition of the structure (all the groups and variables, and optionally attributes) of the file.