gh-91611: Use example.com for documentation, not mydomain.com (GH-91613)

example.com is reserved by the IANA as special-use domain name for documentation
purposes. The domain names are used widely in books, tutorials, sample network
configurations, and generally as examples for the use of domain name.

On the other hand, mydomain.com is real Domain Name Registration service.
(cherry picked from commit ea392467829d6e93f824bde8eb87bdb31d9e4c62)

Co-authored-by: Motoki Naruse <motoki@naru.se>