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/blockprint/server.rs

@@ -0,0 +1,31 @@
+use crate::blockprint::database::{
+    get_blockprint_by_root, get_blockprint_by_slot, WatchBlockprint,
+};
+use crate::database::{get_connection, PgPool, WatchHash, WatchSlot};
+use crate::server::Error;
+
+use axum::{extract::Path, routing::get, Extension, Json, Router};
+use eth2::types::BlockId;
+use std::str::FromStr;
+
+pub async fn get_blockprint(
+    Path(block_query): Path<String>,
+    Extension(pool): Extension<PgPool>,
+) -> Result<Json<Option<WatchBlockprint>>, Error> {
+    let mut conn = get_connection(&pool).map_err(Error::Database)?;
+    match BlockId::from_str(&block_query).map_err(|_| Error::BadRequest)? {
+        BlockId::Root(root) => Ok(Json(get_blockprint_by_root(
+            &mut conn,
+            WatchHash::from_hash(root),
+        )?)),
+        BlockId::Slot(slot) => Ok(Json(get_blockprint_by_slot(
+            &mut conn,
+            WatchSlot::from_slot(slot),
+        )?)),
+        _ => Err(Error::BadRequest),
+    }
+}
+
+pub fn blockprint_routes() -> Router {
+    Router::new().route("/v1/blocks/:block/blockprint", get(get_blockprint))
+}