Update Company Model - Githubissues

Description

The company model is outdated wrt to the frontend requirements. Update the model along with any relevant tests and endpoints.

[ ] add an image field for the company profile
[ ] alter the array of persons Ids to have required: false (an initial company doesn't require list of employees)
[ ] update company database services according to the model changes and test it
[ ] update the /companies endpoints and test it
[ ] any other changes made as per the frontend requirements, e.g. might not need organisation field for Person now