Define log location; mask API credentials

[n7studios]

Summary

Adds a debugLogFileLocation parameter to the class constructor, allowing developers to specify where the log file should be written to, instead of the default src/logs/debug.log, which may be public facing.

Masks the API Key and Secret in the log file if detected in the create_log() message.

Testing

• testDebugEnabledWithCustomLogFile: Test that debug logging works when enabled, a custom debug log file and path is specified and an API call is made.
• testDebugAPIKeyAndSecretAreMasked: Test that debug logging works when enabled and an API call is made, with the API Key and Secret masked in the log file.

Checklist

• I have written a test and included it in this PR
• I have run all tests and they pass
• The code passes when running the PHP CodeSniffer
• The code passes when running PHPStan
• I have assigned a reviewer or two to review this PR (if you're not sure who to assign, we can do this step for you)