This commit introduces a new (composable) trait; a NamespaceResolver is
an abstraction responsible for taking a string namespace from a user
request, and mapping to it's catalog ID.
This allows the NamespaceId to be injected through the DmlHandler chain
in addition to the namespace name.
As part of this change, the NamespaceAutocreation layer was changed from
an implementator of the DmlHandler trait, to a NamespaceResolver as it
is a more appropriate abstraction for the functionality it provides.
This doesn't really need to be fallible but forces propagation of a ton
of error handling - no shards is always a sign of something being very
wrong, and can be caught in the caller if it's for some reason an
acceptable state / can be recovered from.
Went through and remove all lazy_static uses with once_cell (while waiting for the project to compile). There are still dependencies using lazy_static so it is still in the crate graph but at least there isn't an explicit dependency on it (and it is easier to update to `std::lazy::Lazy` once that is stable).
Andrew Lamb
Carol (Nichols || Goulding)
Dom Dwyer
Markus Westerlind