Update the config for Cox Communications and Yahoo to reflect migration

[Brendan Abolivier]

Migrated from Bugzilla (https://bugzilla.mozilla.org/show_bug.cgi?id=1884549)

Initial message from the reporter:

Cox are currently in a migration of all their email account to Yahoo.
While information beyond that linked to is in short supply, the information in the ISP database is already out of date for some and will soon be out of date for all the Cox email users.

I have not seen the email from Cox, but previous experience would indicate that yahoo will be advising folk to use the new account wizard for the transition, ad that sounds like what occured here https://support.mozilla.org/en-US/questions/1441949. Creating new account is what they have advised in the past for similar transitions and from my observations in bug 1884548 modifying your account settings is not a simple process that I would be prepared to recommend any longer.

I have asked the user in the support topic for a copy of the email they received to initiate their changes, if I receive it I will attach the content to this bug for informational purposes.

We currently host a config for Cox here: https://github.com/thunderbird/autoconfig/blob/f254b7d2b043a2b91b99e22633e56284ffe5a4fd/ispdb/cox.net.xml

Information on the migration from Cox's website: https://www.cox.com/residential/support/coxnet-email-transitioning-to-yahoo.html

My understanding is that the migration is still ongoing, so unsure what our timings should be with regards to updating existing configs - we might want to wait till it's fully done. But then, I don't believe Cox has published any information regarding a deadline for their users to migrate their accounts.