add a postgres history backend (#2322)

Postgres support is behind a build tag; use `make build_full`
or `make install_full` to compile it in.

.github/workflows/build.yml

@@ -22,6 +22,8 @@ jobs:
           go-version: "1.26"
       - name: "install python3-pytest"
         run: "sudo apt install -y python3-pytest python3-websockets"
+      - name: "make build_full"
+        run: "make build_full"
       - name: "make install"
         run: "make install"
       - name: "make test"