Add `description` field to system types

[joelvdavies]

For the purposes of knowing what a system type means and how its used. (#557 (comment))

• Field should probably be optional

[lottieo]

currently: system type model and schema only contain id and value fields
want: description field, should be optional, is set by user

changes in files

• model
• schema
• cli/create
• cli/update
• scripts/setup.mongodb line 52
• scripts/generate_mock_data

other

• to update data/mock_data.dump, run generating new mock data command in the README

doesn't require testing, but may break some e2e tests

tests

• fix unit tests
• fix e2e tests

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notes

typer used for command line things
prompt.ask, asks user in terminal, is optional

in cli/update - autofill description with pre-exisiting description?
use rich for colours and emojis in console

rules

(part of v3)
system types needed to define rules
create, move, delete cannot happen without a rule permitting it