Improve license activation messages

[jakejackson1]

Description

TODO:

• [x] Unit tests
• [x] 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:

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

Additional Comments

[codecov[bot]]

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 :warning:
src/Helper/Helper_Abstract_Options.php	0.00%	2 Missing :warning:

Additional details and impacted files

```diff @@ 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 ```

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