Add a shared credentials relationship from nextinpact.com to next.ink

[ChristopheLav]

Overall Checklist

• [x] I agree to the project's Developer Certificate of Origin
• [x] The top-level JSON objects are sorted alphabetically
• [x] There are no open pull requests for the same update

for shared-credentials.json

• [x] There's evidence the domains are currently related (SSL certificates, DNS entries, valid links between sites, legal documents etc.)
• [x] If using shared, the new group serves login pages on each of the included domains, and those login pages accept accounts from the others. (nextinpact.com has transitioned their domain to next.ink since a few months)
• [x] If using from and to, the new group, the from domain(s) redirect to the to domain to log in.