add saved queries and exports to latest

[dave-connors-3]

closes #126

This PR adds support for SQEs for latest version of dbt. I used the docs here to guide implementation.

Two areas for discussion that i don't feel strongly about:

• i added cache as an available value in exports' export_as field based on the docs saying "coming soon", but I am very willing to remove it until it's actually available .
• i let additionalProperties: True for export configs assuming that there will be more configs over time. I can make this more restrictive if we want

sorry for the unintentional whitespace edits 😅