MailChimp API Keys doc page is outdated

[DAcodedBEAT]

The new URL is https://mailchimp.com/help/about-api-keys/

Tracking issue for:

• [ ] https://github.com/ChurchCRM/CRM/security/code-scanning/95
• [ ] https://github.com/ChurchCRM/CRM/security/code-scanning/115

note: should also update wiki

see: https://github.com/search?q=repo%3AChurchCRM%2FCRM+kb.mailchimp.com&type=code

[Deepakchowdavarapu]

Hey @DAcodedBEAT I'd like to work on this issue , please assign it to me.