Add docker compose file

[evanofslack]

Including a containerized Rocket.Chat instance will help to standardize development and testing for this project going forward. It will also enable automated CI/CD with Github actions in the future.

The included docker-compose.yml is very similar to the recommended configuration. The main additions are env variables to disable rate limiting.

[geekgonecrazy]

left a few suggestions. Lets try to use mongo 5.0 images so Rocket.Chat doesn't fuss when starting up

[evanofslack]

@geekgonecrazy Good call, changed the Mongo version

[CLAassistant]

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:white_check_mark: evanofslack
:x: evan slack

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