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/postgres_docker_compose/compose.yml

@@ -0,0 +1,16 @@
+version: "3"
+
+services:
+    postgres:
+        image: postgres:12.3-alpine
+        restart: always
+        environment:
+            POSTGRES_PASSWORD: postgres
+            POSTGRES_USER: postgres
+        volumes:
+            - postgres:/var/lib/postgresql/data
+        ports:
+            - 127.0.0.1:5432:5432
+
+volumes:
+    postgres: