Add support link to DNS status check failure message

[jacobd91]

This PR simply adds a link to the error message if the DNS status check comes back as not pointing to the CDN

The link won't work as the article is still a draft, but the slugs have been synced so once it's published the link should work correctly. Here is the link to the draft article https://www.boldgrid.com/support/?p=164753&preview=true

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 25 lines in your changes missing coverage. Please review.
✅ Project coverage is 2.28%. Comparing base (754eb42) to head (7db0219).

Files with missing lines	Patch %	Lines
Cdnfsd_TotalCdn_Page.php	0.00%	18 Missing ⚠️
Cdnfsd_TotalCdn_Status_Dns.php	0.00%	7 Missing ⚠️

Additional details and impacted files

@@                   Coverage Diff                   @@
##             total-cdn-staging    #1225      +/-   ##
=======================================================
- Coverage                 2.28%    2.28%   -0.01%     
  Complexity               20202    20202              
=======================================================
  Files                      669      669              
  Lines                   102021   102039      +18     
=======================================================
  Hits                      2335     2335              
- Misses                   99686    99704      +18     

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[cssjoe]

See comment.

Also, the article says to update "www" in step 2 and the "apex" in step 3. We want to make it clear that they would do one or the other, depending on their siteurl hostname.