Add caching layer

[mjirv]

As a user I want my queries to be lightning fast and am often willing to tolerate a small chance that the data will be slightly out of date.

To solve, implement a caching layer that:

1. Allows the user to configure a cache expiration time as an env variable, and uses a reasonable default if none is given (say, 1 day)
2. When a query comes in, checks if it has been run within the expiration window
3. If so, use a cached version of the results and avoid hitting dbt at all
4. Queries should have an optional parameter to force no cache for cases when the user really wants the latest data

[mjirv]

We should consider security implications, see e.g. https://getdbt.slack.com/archives/C02CCBBBR1D/p1646869075342249?thread_ts=1646751849.912379&cid=C02CCBBBR1D