Add a new table to nars for derivation source files

This will allow serving the nars for derivation source files.

sqitch/deploy/add_derivation_source_file_nars.sql

@@ -0,0 +1,14 @@
+-- Deploy guix-data-service:add_derivation_source_file_nars to pg
+
+BEGIN;
+
+CREATE TABLE derivation_source_file_nars (
+    derivation_source_file_id integer PRIMARY KEY REFERENCES derivation_source_files (id),
+    compression varchar NOT NULL,
+    hash_algorithm varchar NOT NULL,
+    hash varchar NOT NULL,
+    uncompressed_size integer NOT NULL,
+    data bytea NOT NULL
+);
+
+COMMIT;

sqitch/revert/add_derivation_source_file_nars.sql

@@ -0,0 +1,7 @@
+-- Revert guix-data-service:add_derivation_source_file_nars from pg
+
+BEGIN;
+
+DROP TABLE derivation_source_file_nars;
+
+COMMIT;

sqitch/sqitch.plan

@@ -39,3 +39,4 @@ add_some_database_indexes 2019-12-05T15:53:04Z Christopher Baines <mail@cbaines.
 derivation_output_sets 2019-12-05T23:19:05Z Christopher Baines <mail@cbaines.net> # Describe the sets of derivation outputs
 builds_add_derivation_output_details_set_id 2019-12-07T18:25:38Z Christopher Baines <mail@cbaines.net> # Add a derivation_output_details_set_id column to builds
 derivations_hash_index 2019-12-24T22:54:19Z Christopher Baines <mail@cbaines.net> # Add index on derivations for the hash component of the filename
+add_derivation_source_file_nars 2019-12-28T20:37:06Z Christopher Baines <mail@cbaines.net> # Add table for derivation source file nars

sqitch/verify/add_derivation_source_file_nars.sql

@@ -0,0 +1,7 @@
+-- Verify guix-data-service:add_derivation_source_file_nars on pg
+
+BEGIN;
+
+-- XXX Add verifications here.
+
+ROLLBACK;