Add the post-portal tech email to the internet-header docs

[oliverschuerch]

If a new project needs to use the internet-header component, the post-portal team must create a header config in there solution. To let them know, a project is in the need for such a config, they must be informed by email. The idea is to add this email and a short description to our internet-header docs.

### Tasks
- [x] Ask the post-portal team if it's ok to add the email to our internet-header docs and point out, that this information is public for everyone.
- [x] Add a short description, which information needs to be sent and add the email address as a mailto link (do this only if the post-portal team agrees).
- [ ] https://github.com/swisspost/design-system/issues/3672

[gfellerph]

Asked for infos on this one

[gfellerph]

Step 1: Integration of header only: contact dm-tec@post.ch directly Integration of header and KLP: contact KLP first for integration

Step 2: Provide these informations to DM Tec:

• ServiceID (ProjektID)
• Languages which you'd like to support
• Allowed referrers per environment (test/int/prod)
• Categories for the Online Service (see https://www.post.ch/de/kundencenter/onlinedienste#t=AllOSTab&sort=%40servicez32xname%20ascending for a list)
• Name of the Online Service in all available languages
• URLs of all environments and languages (links should be dependent on language)
• Abstract in all available languages (will be shown on https://www.post.ch/de/kundencenter/onlinedienste#t=AllOSTab&sort=%40servicez32xname%20ascending)