Plaid sync domain improvements (#2267)

Breaks our Plaid sync process out into more manageable classes. Notably, this moves the sync process to a distinct, 2-step flow:

1. Import stage - we first make API calls and import Plaid data to "mirror" tables
2. Processing stage - read the raw data, apply business rules, build internal domain models and sync balances

This provides several benefits:

- Plaid syncs can now be "replayed" without fetching API data again
- Mirror tables provide better audit and debugging capabilities
- Eliminates the "all or nothing" sync behavior that is currently in place, which is brittle

test/fixtures/accounts.yml

@@ -24,9 +24,10 @@ depository:
 
 connected:
   family: dylan_family
-  name: Connected Account
+  name: Plaid Depository Account
   balance: 5000
   currency: USD
+  subtype: checking
   accountable_type: Depository
   accountable: two
   plaid_account: one

test/fixtures/plaid_accounts.yml

@@ -1,3 +1,9 @@
 one:
+  current_balance: 1000
+  available_balance: 1000
+  currency: USD
+  name: Plaid Depository Account
   plaid_item: one
-  plaid_id: "1234567890"
+  plaid_id: "acc_mock_1"
+  plaid_type: depository
+  plaid_subtype: checking

test/fixtures/plaid_items.yml

@@ -1,5 +1,7 @@
 one:
   family: dylan_family
-  plaid_id: "1234567890"
+  plaid_id: "item_mock_1"
   access_token: encrypted_token_1
-  name: "Test Bank"
+  name: "Test Bank"
+  billed_products: ["transactions", "investments", "liabilities"]
+  available_products: []