feat: enforce entity name requirements

[austince]

As per the ES index naming requirements, this PR brings in validation to entity types, based on the ES implementation. This enforces the name requirements on create and update model methods, which is aligned with Elasticsearch's somewhat lenient handling of index names:

DELETE -someindex # returns 404 not found

GET -someindex # returns 404 not found

PUT -someindex  # returns 400 validation error
{}

Closes #58

[austince]

Sorry about the repeated pushes, keep committing pieces of our fork 🤦🏼‍♂️ should be final now.

[austince]

Rebasing to fix conflicts..

[davemoore-]

LGTM!