Upgrade to Go 1.18 and update dependencies

[amarpal]

Changes in this PR

This pull request upgrades the project to Go 1.18 and includes several important updates:

1. Upgraded to Go 1.18 and updated all dependencies
2. Removed deprecated TLS config methods for Go 1.14+ compatibility
3. Removed deprecated x509 PEM encryption functions for security reasons

These changes aim to improve the project's security, compatibility, and take advantage of the latest features and improvements in Go 1.18.

Upgrade details

• The project has been updated to use Go 1.18
• All dependencies have been updated to their latest compatible versions
• Deprecated TLS configuration methods have been removed to ensure compatibility with Go 1.14 and newer versions
• Deprecated x509 PEM encryption functions have been removed to enhance security

Please review these changes carefully, especially the removal of deprecated functions, to ensure they don't negatively impact any existing functionality.

[BenNolanGartner]

Hi @sideshow! There's a CVE in golang-jwt v4 (CVE-2025-30204), which this PR updates the usage of here to v5. Is there any chance it could be merged?