Configures a plumber2 API to serve htmxr's static assets
(htmx JavaScript library) at /htmxr/assets/.
Examples
plumber2::api() |>
hx_serve_assets()
#> ── A plumber server ────────────────────────────────────────────────────────────
#> Serving on http://127.0.0.1:8080
#> Currently not running
