Integrated heat storage and e-conversion asset

[FJanssen-TNO]

Start on creating an integrated heat storage asset that can be charged using electricity.
Using a heatbuffer with an additional electricity port.

• Check setup
• Add the parsing of the new relevant efficiencies --> e.g. charging efficiency (conversion of e to heat)
• Check that still efficiency of the buffer can be set, e.g. self discharge rate or something else.
• Add test
• Update changelog