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/server/config.rs

@@ -0,0 +1,28 @@
+use serde::{Deserialize, Serialize};
+use std::net::IpAddr;
+
+pub const LISTEN_ADDR: &str = "127.0.0.1";
+
+pub const fn listen_port() -> u16 {
+    5059
+}
+fn listen_addr() -> IpAddr {
+    LISTEN_ADDR.parse().expect("Server address is not valid")
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct Config {
+    #[serde(default = "listen_addr")]
+    pub listen_addr: IpAddr,
+    #[serde(default = "listen_port")]
+    pub listen_port: u16,
+}
+
+impl Default for Config {
+    fn default() -> Self {
+        Self {
+            listen_addr: listen_addr(),
+            listen_port: listen_port(),
+        }
+    }
+}