[Fleet] Make preconfiguration space-aware

[kpollich]

As part of the RBAC project, Fleet users will begin segmenting data into different spaces. Fleet saved objects will have the single namespace type, and thus objects with the same ID will be able to exist in multiple spaces at once. For preconfiguration, this means that when Fleet setup runs in a non-default space, we will not detect agent/package policies exist, and create them again even if they already exist in the default space.

The preconfiguration schema should be updated to support creating objects in certain spaces by providing a space ID, and we should assume the default space if an ID is not explicitly provided. Objects should not be recreated if they already exist in the default space.

[elasticmachine]

Pinging @elastic/fleet (Team:Fleet)