feat(email/oauth): implement OAuth2 support for Gmail provider (#212)

db/migrations/0028_email_oauth_tokens.down.sql

@@ -0,0 +1 @@
+DROP TABLE IF EXISTS email_oauth_tokens;

db/migrations/0028_email_oauth_tokens.up.sql

@@ -0,0 +1,17 @@
+-- 0028_email_oauth_tokens
+-- Store OAuth2 tokens for Gmail email providers.
+
+CREATE TABLE IF NOT EXISTS email_oauth_tokens (
+  id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+  email_provider_id UUID NOT NULL UNIQUE REFERENCES email_providers(id) ON DELETE CASCADE,
+  email_address TEXT NOT NULL DEFAULT '',
+  access_token TEXT NOT NULL DEFAULT '',
+  refresh_token TEXT NOT NULL DEFAULT '',
+  expires_at TIMESTAMPTZ,
+  scope TEXT NOT NULL DEFAULT '',
+  state TEXT NOT NULL DEFAULT '',
+  created_at TIMESTAMPTZ NOT NULL DEFAULT now(),
+  updated_at TIMESTAMPTZ NOT NULL DEFAULT now()
+);
+
+CREATE INDEX IF NOT EXISTS idx_email_oauth_tokens_state ON email_oauth_tokens(state) WHERE state != '';