Add shared credentials for DynDNS (dyndns.com, dyndns.org → account.dyn.com)

[mangeshraut712]

Bar check: This meets the shared-credentials bar. DynDNS and the Dyn account portal are the same account. dyndns.com and dyndns.org redirect to account.dyn.com, which returns 200 with title "My Dyn Account" and a password field, and a nonexistent path on that host returns 404. A password saved on dyndns.com or dyndns.org is the password for that same Dyn account on account.dyn.com.

Both old apexes redirect away, so they are marked obsolete. dyn.com itself now redirects to Oracle DNS marketing, so the target is the account host account.dyn.com rather than dyn.com or oracle.com.

Evidence, checked live:

• https://dyndns.com/account/login → 302 https://account.dyn.com/ → 200, title My Dyn Account, visible text Sign In / Username / Password / Forgot Password?, input name="password" type="password"
• https://dyndns.org/account/login → 302 https://account.dyn.com/ (same password form)
• https://www.dyndns.com/ and https://dyndns.org/ → 302 https://account.dyn.com/
• https://account.dyn.com/this-path-should-not-exist-4a36 → 404, title Dyn.com - Page Not Found
• https://dyn.com/login → Oracle DNS marketing, not this form, so dyn.com is not the shared target

Overall Checklist

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

for shared-credentials.json

• There's evidence the domains are currently related (dyndns.com and dyndns.org redirect to the Dyn account password form)
• If using from and to, the from domain redirects to the to domain to log in