Improve license activation messages

[jakejackson1]

Description

TODO:

• Unit tests
• Update GravityPDF.com and return the license ID in the response

This PR:

• Adds more descriptive text when an activation error occurs.
• Include specific actions to help users get their licenses activated correctly.
• Allow activation on sites marked as non-production

Testing instructions

Install a paid Gravity PDF extension and then test the following:

1. Activate an active license
2. Activate an expired license
3. Activate a disabled license
4. Activate a license that has reached its site limit

Screenshots

Checklist:

• I've tested the code.
• My code is easy to read, follow, and understand
• My code follows the accessibility standards.
• My code has proper inline documentation / docblocks.

Additional Comments

[codecov]

Codecov Report

Attention: Patch coverage is 76.04167% with 23 lines in your changes are missing coverage. Please review.

Project coverage is 77.03%. Comparing base (f27ba77) to head (446897a).

Files	Patch %	Lines
src/Helper/Helper_Abstract_Addon.php	44.73%	21 Missing ⚠️
src/Helper/Helper_Abstract_Options.php	0.00%	2 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff               @@
##           development    #1496      +/-   ##
===============================================
- Coverage        77.03%   77.03%   -0.01%     
===============================================
  Files              243      243              
  Lines            12447    12509      +62     
  Branches           370      370              
===============================================
+ Hits              9589     9636      +47     
- Misses            2850     2865      +15     
  Partials             8        8              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.