Allow filter functions to be async

[b3nn0]

Hi,
this is a simple PR that adds an "await" around the filter function calling.

Motivation:

This allows especially the fn filter to define an async function.
This can be very useful, e.g. if you want to plot the result of a service call directly, without having to create intermediate template sensors just to deliver data to the frontend.
intermediate template sensors are sometimes not great when you want to display a lot of data, since the amount of bytes a state or state attributes can have is very limited (state 255 bytes AFAIK, and state attributes 16kb).
This limitation is there for a good reason: home-assistant/core#149316 (comment)

Also, they fill up your recorder with information that might not be desirable to be stored long term.

With this PR, it is now possible to do this:

    filters:
      - fn: |-
          async ({xs, ys, meta, hass}) => {
            const weather = await hass.callService("weather", "get_forecasts", {type: "hourly"}, {entity_id:"weather.home"}, true, true)
            const home = weather.response["weather.home"].forecast
            return {
              xs: home.map(h => new Date(h.datetime)),
              ys: home.map(h => h.temperature)
            }
          }