Implement target path diagram for 2035 zero emissions goal

[Philzen]

The demands of the initiative Klimabegehren Flensburg were unanimously accepted by the local government (which is the 100 % shareholder of Stadtwerke Flensburg) in December 2022.

Therefore we should have a target path diagram, analogous to the greenco₂ncept diagram, to be able to follow its implementation vs. actual carbon emissions.