Set up new tables in Hasura to support the rewards flow

[philhawksworth]

• [x] Create the achievements table in Hasura
• [x] Create rewards table in Hasura
• [x] Create relationships between achievements and rewards tables so we can query in GraphQL
• [x] Register a webhook in Hasura to run whenever the activity table gets new data (ref #471)

[tzmanics]

Ok, i deleted my last long comment to avoid any confusion.

The rewards table is now set up correctly (thank you @jlengstorf) so that it has a column for achievement_id that has an object relationship to id in the achievements table.

The achievements table never needs to know any information about rewards so no new columns were added but it's id now has an array relationship to achievement_id in the rewards table.

Next steps:

• work on #468 to write to the achievement table every time it’s triggered (for now).
• make a new event trigger (like the jamstack-exploreres-check-achievement one) that will grab the achievement_id (will get sent to the reward webhook as part of the event payload) and write to the rewards table.