fix: Add x509 key pair to config

[DavidMiserak]

This pull request adds support for using x509 certificate key pairs for TLS connections in the fluent package. It introduces new configuration options for specifying certificate and key files, updates the connection logic to use these files if provided, and documents the change in the changelog.

TLS/x509 certificate support:

• Added TlsCertFile and TlsKeyFile fields to the Config struct, allowing users to specify paths to x509 certificate and key files.
• Updated the TLS connection logic in the connect method to load and use the specified x509 certificate and key pair if both are provided.
• Introduced default values for the new certificate and key file configuration options.
• Ensured the new config options are set to their defaults if not specified by the user during initialization.

Documentation:

• Updated CHANGELOG.md to reflect the addition of x509 key pair support.