Add config parser tests for SSLCerts

[john-david3]

Proposed changes

• Added test to make sure config parser is correctly parsing SSL Certs
• Added tests to check if parser handles multiple certs correctly
• Created test config files
• Added new embed in nginx_config.go

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING document
• I have run make install-tools and have attached any dependency changes to this pull request
• If applicable, I have added tests that prove my fix is effective or that my feature works
• If applicable, I have checked that any relevant tests pass after adding my changes
• If applicable, I have updated any relevant documentation (README.md)
• If applicable, I have tested my cross-platform changes on Ubuntu 22, Redhat 8, SUSE 15 and FreeBSD 13