Add light sync command

- Only syncs block headers (excludes block bodies, transactions, receipts, and logs)
- Modifies validation window to include the most recent block
- Isolates validation window to the variable defined in the cmd directory (blocks
  have a separate variable defined in the block_repository for determining when
  to set a block as final)

db/schema.sql

@@ -121,6 +121,40 @@ CREATE TABLE public.eth_nodes (
 );
 
 
+--
+-- Name: headers; Type: TABLE; Schema: public; Owner: -
+--
+
+CREATE TABLE public.headers (
+    id integer NOT NULL,
+    hash character varying(66),
+    block_number bigint,
+    raw bytea,
+    eth_node_id integer,
+    eth_node_fingerprint character varying(128)
+);
+
+
+--
+-- Name: headers_id_seq; Type: SEQUENCE; Schema: public; Owner: -
+--
+
+CREATE SEQUENCE public.headers_id_seq
+    AS integer
+    START WITH 1
+    INCREMENT BY 1
+    NO MINVALUE
+    NO MAXVALUE
+    CACHE 1;
+
+
+--
+-- Name: headers_id_seq; Type: SEQUENCE OWNED BY; Schema: public; Owner: -
+--
+
+ALTER SEQUENCE public.headers_id_seq OWNED BY public.headers.id;
+
+
 --
 -- Name: log_filters; Type: TABLE; Schema: public; Owner: -
 --
@@ -385,6 +419,13 @@ ALTER TABLE ONLY public.blocks ALTER COLUMN id SET DEFAULT nextval('public.block
 ALTER TABLE ONLY public.eth_nodes ALTER COLUMN id SET DEFAULT nextval('public.nodes_id_seq'::regclass);
 
 
+--
+-- Name: headers id; Type: DEFAULT; Schema: public; Owner: -
+--
+
+ALTER TABLE ONLY public.headers ALTER COLUMN id SET DEFAULT nextval('public.headers_id_seq'::regclass);
+
+
 --
 -- Name: log_filters id; Type: DEFAULT; Schema: public; Owner: -
 --
@@ -459,6 +500,14 @@ ALTER TABLE ONLY public.eth_nodes
     ADD CONSTRAINT eth_node_uc UNIQUE (genesis_block, network_id, eth_node_id);
 
 
+--
+-- Name: headers headers_pkey; Type: CONSTRAINT; Schema: public; Owner: -
+--
+
+ALTER TABLE ONLY public.headers
+    ADD CONSTRAINT headers_pkey PRIMARY KEY (id);
+
+
 --
 -- Name: logs logs_pkey; Type: CONSTRAINT; Schema: public; Owner: -
 --
@@ -574,6 +623,14 @@ ALTER TABLE ONLY public.token_supply
     ADD CONSTRAINT blocks_fk FOREIGN KEY (block_id) REFERENCES public.blocks(id) ON DELETE CASCADE;
 
 
+--
+-- Name: headers eth_nodes_fk; Type: FK CONSTRAINT; Schema: public; Owner: -
+--
+
+ALTER TABLE ONLY public.headers
+    ADD CONSTRAINT eth_nodes_fk FOREIGN KEY (eth_node_id) REFERENCES public.eth_nodes(id) ON DELETE CASCADE;
+
+
 --
 -- Name: blocks node_fk; Type: FK CONSTRAINT; Schema: public; Owner: -
 --