Improve Signed PDF Log Messages and Self-Heal Secret Key

[jakejackson1]

Description

Fixes https://github.com/GravityPDF/gravity-pdf/issues/1534

Also, instead of throwing an exception that stops the process, we'll regenerate the secret key if we ever detect it has been corrupted.

Checklist:

• [x] I've tested the code.
• [x] 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 92.85714% with 2 lines in your changes missing coverage. Please review.

Project coverage is 76.07%. Comparing base (6f597f1) to head (b11441b). Report is 1 commits behind head on development.

Files	Patch %	Lines
src/Helper/Helper_Url_Signer.php	89.47%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## development #1547 +/- ## =============================================== + Coverage 76.03% 76.07% +0.03% =============================================== Files 248 248 Lines 12949 12973 +24 Branches 370 370 =============================================== + Hits 9846 9869 +23 - Misses 3095 3096 +1 Partials 8 8 ```

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