multi: add sqlc support

sqlc is a tool that generates fully type-safe idiomatic code from SQL.
The result is Go code can then used execute the queries in the database.

The noraml flow looks like:
- The developer write some sql that will update the schema in the
  database: new tables, indices, etc
- The developer updates the set of queries that will use the new schema.
- `sqlc` generates type-safe interfaces to those queries.
- The developer can then write application code that calls the methods
  generated by sqlc.

The tool configuration needs to live in the repo's root and its name is
`sqlc.yaml`.

LND will support out of the box sqlite and postgres. The sql code needs to
be (almost) the same for both engines, so we cannot use custom functions
like `ANY` in postgres.

The SQLC config file needs to define what is the target engine, we will
set postgres but the generated code can be executed by sqlite too.

In some specific cases, we will `match and replace` some sql lines to be
sure the table definitions are valid for the targeted engine.

Makefile

@@ -249,6 +249,14 @@ list:
 		grep -v Makefile | \
 		sort
 
+sqlc:
+	@$(call print, "Generating sql models and queries in Go")
+	./scripts/gen_sqlc_docker.sh
+
+sqlc-check: sqlc
+	@$(call print, "Verifying sql code generation.")
+	if test -n "$$(git status --porcelain '*.go')"; then echo "SQL models not properly generated!"; git status --porcelain '*.go'; exit 1; fi
+
 rpc:
 	@$(call print, "Compiling protos.")
 	cd ./lnrpc; ./gen_protos_docker.sh

scripts/gen_sqlc_docker.sh

@@ -0,0 +1,19 @@
+#!/bin/bash
+
+set -e
+
+# Directory of the script file, independent of where it's called from.
+DIR="$(cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd)"
+# Use the user's cache directories
+GOCACHE=`go env GOCACHE`
+GOMODCACHE=`go env GOMODCACHE`
+
+echo "Generating sql models and queries in go..."
+
+docker run \
+  --rm \
+  --user "$UID:$(id -g)" \
+  -e UID=$UID \
+  -v "$DIR/../:/build" \
+  -w /build \
+  kjconroy/sqlc:1.18.0 generate

sqlc.yaml

@@ -0,0 +1,10 @@
+version: "2"
+sql:
+  - engine: "postgresql"
+    schema: "sqldb/sqlc/migrations"
+    queries: "sqldb/sqlc/queries"
+    gen:
+      go:
+        out: sqldb/sqlc
+        package: sqlc
+        emit_interface: true