Add dataviz

[kimadactyl]

User story

As a comissioner, I need to be able to make cool graphs of PlaceCal data so that I can make fancy dashboards to sell it with to my organisation.

As a developer, I want to make some visualisations of the data coming in so we can see how the platform is doing and how we might need to plan for performance

Acceptance criteria

• [ ] Metabase running locally and instructions added to README for how to set it up
• [x] Metabase running on staging and instructions for how to do this
• [x] Metabase running on production

Implementation notes & questions

Metabase selected for this as it's open source, and runs directly on the server.

This might do a bit to alleviate the pressure on #1215 as it'll be a while before we get on it

Others considered:

• Tableau: very expensive, adapter code buggy, possibly overkill functioanlity wise for now
• PowerBI: not getting into Microsoft stuff for this

Implementation plan

To be written by the developer

[lexiwitch]

Done and documented here: https://www.notion.so/gfsc/Deploying-Metabase-HOWTO-dcadf395f2bb433e829cc10cba4aca54