query DEP names

[jessepeterson]

Implement querying DEP names. This includes:

• Generic interfaces & structs for list-returning queries (i.e. pagination, etc.)
• Storage implementations for mysql, pgsql, inmem and filekv backends
• Simple test coverage
• Documentation & OpenAPI spec updates.

While perhaps overkill this implements some of the recent discussion around pagination and filtering queries in the generic form.

Notes:

• The legacy file backend test was removed because an erroring stub function to meet the interface is created. We'll remove the file backend in another PR to keep intents separated.

[jessepeterson]

@korylprince hopefully parts of this can serve as a model for e.g. micromdm/nanomdm#214.

[jessepeterson]

Note this also gets closer for #47 by having an interface for querying DEP names.

[korylprince]

LGTM