Add configuration for local test bot/workspace

[rebkwok]

I (@rebkwok) have a test workspace and test bot set up; it should be possible to store credentials in bitwarden and template them into an env file as we do on other projects, which would avoid everyone having to go through the laborious process described in DEPLOY.md to set up their own local test environment.

[rebkwok]

A candidate for the next round of deck scrubbing - I'm pretty sure I'm the only one who runs an entire test workspace/bot/dispatcher locally when adding new things to bennett bot because the setup is a bit fiddly