determine logic for when achievement unlocked

[philhawksworth]

We'll most likely maintain a list of achievement criteria and associated rewards. I propose that the initial achievement we use to prove the end-to-end flow is:

Achievement	Reward
Complete one mission	Explorers sticker pack

[jlengstorf]

current thoughts on the logic here, which would be triggered on each dashboard page load:

1. check for achievement events attached to the current user
2. if found (for now, since there's only one) short-circuit and display the UI described in #455
3. if not, check for whether the user has completed any missions
4. if not, do nothing
5. if they have completed a mission, create a new achievement and send that off
6. display the UI

later on, we'll need to revisit this for additional achievements, but this should get us up and running

[tzmanics]

Is this technically closed with this miro mind map @jlengstorf https://miro.com/app/board/o9J_lWmoARA=/