agent enrollment store implementation (#967)

controller/store/sql/postgresql/033_v1_0_5_agent_enrollments.sql

@@ -0,0 +1,14 @@
+-- +migrate Up
+
+create table agent_enrollments (
+    id                  serial                  primary key,
+
+    environment_id      integer                 not null references environments(id),
+    token               varchar(32)             not null unique,
+
+    created_at          timestamptz             not null default(current_timestamp),
+    updated_at          timestamptz             not null default(current_timestamp),
+    deleted             boolean                 not null default(false)
+);
+
+create index agent_enrollments_environment_id_idx on agent_enrollments(environment_id);