Add beacon.watch (#3362)

> This is currently a WIP and all features are subject to alteration or removal at any time.

## Overview

The successor to #2873.

Contains the backbone of `beacon.watch` including syncing code, the initial API, and several core database tables.

See `watch/README.md` for more information, requirements and usage.

watch/src/database/utils.rs

@@ -0,0 +1,29 @@
+#![allow(dead_code)]
+use crate::database::config::Config;
+use diesel::pg::PgConnection;
+use diesel::prelude::*;
+use diesel_migrations::{FileBasedMigrations, MigrationHarness};
+
+/// Sets `config.dbname` to `config.default_dbname` and returns `(new_config, old_dbname)`.
+///
+/// This is useful for creating or dropping databases, since these actions must be done by
+/// logging into another database.
+pub fn get_config_using_default_db(config: &Config) -> (Config, String) {
+    let mut config = config.clone();
+    let new_dbname = std::mem::replace(&mut config.dbname, config.default_dbname.clone());
+    (config, new_dbname)
+}
+
+/// Runs the set of migrations as detected in the local directory.
+/// Equivalent to `diesel migration run`.
+///
+/// Contains `unwrap`s so is only suitable for test code.
+/// TODO(mac) refactor to return Result<PgConnection, Error>
+pub fn run_migrations(config: &Config) -> PgConnection {
+    let database_url = config.clone().build_database_url();
+    let mut conn = PgConnection::establish(&database_url).unwrap();
+    let migrations = FileBasedMigrations::find_migrations_directory().unwrap();
+    conn.run_pending_migrations(migrations).unwrap();
+    conn.begin_test_transaction().unwrap();
+    conn
+}