Wire subscribe-to-updates in compliance portal

Visitors can subscribe after sign-in via the Updates
CTA or user menu. Also add trust signOut so Log out
works from the menu.

Signed-off-by: Émile Ré <emile@probo.com>

pkg/server/api/trust/v1/graphql/auth.graphql

@@ -5,6 +5,7 @@ extend type Mutation {
     @authentication(required: OPTIONAL)
   updateFullName(input: UpdateFullNameInput!): UpdateFullNamePayload
     @authentication(required: PRESENT) @sessionOnly
+  signOut: SignOutPayload! @authentication(required: PRESENT) @sessionOnly
 }
 
 input SendMagicLinkInput {
@@ -31,3 +32,7 @@ input UpdateFullNameInput {
 type UpdateFullNamePayload {
   success: Boolean!
 }
+
+type SignOutPayload {
+  success: Boolean!
+}