Display notice to admins about D7 EOL, link to Acquia

An EOL notice was added to 7.x-3.9. It's out of date now, so attached is a patch to address that. Note that this patches a different file, the install file, and it shows up in the system status report.

Patch has been added to our private repository, will get pushed in the next batch of commits.

This update was committed to 7.x-4.x .. what's the plan for a release from that branch? The current recommended release is still 7.x-3.11 and that still has the outdated EOL info.

The update says "Drupal 7 will be end of life on November 1, 2023" but it's actually not quite as simple as that; perhaps it'd be good to link to https://www.drupal.org/psa-2022-02-23 where the plan is explained in more detail (and which should get updated if and when anything changes).

I'd also question whether this is accurate:

      $requirements['acquia_agent_eol'] = [                                        
        'title' => t('Acquia Agent module'),                                       
        'value' => t('The 7.x version is EOL!'),                                   
        'description' => $msg,                                                     
        'severity' => REQUIREMENT_WARNING,                                         
      ];

Does this mean the 7.x branch of Drupal core? If so, it's not EOL yet :)

also nit: short array syntax which we avoid in D7 but in this case perhaps it doesn't matter as Acquia's hosting doesn't run PHP 5.x etc..

Suggested patches against both the 7.x-3.x and 7.x-4.x branches.

Hard-coding details of the provisional EOL in November 2023 means it's possible another patch will be necessary in July 2023 when an announcement is due as to whether EOL is confirmed or extended, but the only other option is to link to the PSA and say "go read this" :)