Add shared credentials for TVNOW, auth.rtl.de and rtlplus

[MissesMartinson]

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.)
• rtlplus.de, rtlplus.com, tvnow.at, tvnow.ch redirect to tvnow.de
• the impressum of rtl.de (https://www.rtl.de/cms/service/footer-navigation/impressum.html) and tvnow.de (https://www.tvnow.de/impressum) shows that both domains are part of RTL interactive GmbH
• [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. (For example, we wouldn't use a shared association from google.co.il to google.com, because google.co.il redirects to accounts.google.com for sign in.)
• [ ] If using from and to, the new group, the from domain(s) redirect to the to domain to log in.

[rmondello]

rtlplus.de, rtlplus.com, tvnow.at, tvnow.ch redirect to tvnow.de

Feels like this part should be a from: to:.

[MissesMartinson]

Hey Ricky, thank you for the review. I've changed the type to from...to. Since the old domains are still in use, we set the fromDomainsAreObsoleted-Parameter to false.