check-model-name-contract support for snapshots

[ryancollingwood]

What:

Assuming we consider snapshots equivalent to models for checks purposes then this would be an extension to check-model-name-contract, otherwise it would be a new check something along the lines of check-snapshot-name-contract.

The behaviour would be as implemented for check-model-name-contract:

• On a given directory path
• Find all of the snapshot names (not the filename, but the name of the snapshot as it will be materialised)
• Evaluate if any of them do not match a given regex
• Return 0 on all snapshot names matching, Return 1 if one or more do not pass the regex test

Why

So that I can enforce a convention that all tables that are materialised using the dbt snapshot mechanism follow a convention which makes them easily identifiable - e.g. .*_snapshot

[ryancollingwood]

Had a go at implementing it: #184