Feat-Polyphosphate metabolism

[feiranl]

Description of the issue:

• Gapfilling in polyphosphate metabolism

I hereby confirm that I have:

• [ ] Tested my code with all requirements for running the model
• [ ] Done this analysis in the main branch of the repository
• [ ] Checked that a similar issue does not exist already
• [ ] If needed, asked first in the Gitter chat room about the issue