The CRM app provides the project section that is available by default in each Jira project. This section is intended to show the related Companies and Contacts from the full list of the global section.
You cannot create a new company or contact here, just select ones from the list of existing ones. For each linked company and contact you can specify its role within the project. The linked entries are clickable that allows you to check the information without leaving the project.
There is a special Related Projects attribute available in the Company and Contact templates that display those links if required: