Change to best_soc_keep handling

What's Changed

Features

• New control input_number.predbat_best_soc_keep_weight in expert mode allows you to control how strongly best_soc_keep should be kept to
• Metric keep is not based on the load but on time and amount below the keep threshold.

• Change method of metric keep by @springfall2008 in #1786

Bug fixes

• Bug related to freeze only mode calcs by @springfall2008 in #1785
• Fixed issue where service API calls were not repeated when the charge start/end times change

Testing and tidy up

• Unit testing of inverter started by @springfall2008 in #1782
• Keep step data for debug by @springfall2008 in #1784
• Tidy up some code, debug improvements by @springfall2008 in #1788

Full Changelog: v8.8.13...v8.8.14