Add Remaining Time

[limeryls]

Firstly, really good job ! This repo works fine with my Ecoflow River (EF4 288Wh without extra batterie).
Nevertheless, it could be great to add the remaining time to the available sensors.
As this data is available in the log data, I think it could be added quite easily.

[vwt12eh8]

In the ver2-beta branch under development, the Remain entity was added for a while. However, this value changed frequently during use and polluted the logbook, so it was removed. Now we include Remain as an additional attribute in the Battery entity.

[vwt12eh8]

After some rethinking, I decided to bring back the Remain entity. However, it is disabled by default as it does not solve the problem of overwhelming the database. If you use it, we recommend that you include the following measures in your configuration.yaml

recorder:
  exclude:
    entities:
      - sensor.river_xxxxxx_remain