added custom CA support in dispatcher and server for secure TLS connections

[mekilis]

Support for Custom CA Certificates in Dispatcher

Overview

This feature is particularly useful for customers who need to interact with internal services behind a VPN or private infrastructure using self-signed certificates.

Configuration

Users can specify a custom CA certificate in the Dispatcher configuration using either a file path or a direct certificate string.

Dispatcher Configuration Fields

• CACertPath: Path to the CA certificate file (PEM format). This certificate will be added to the trusted root CA pool.
• CACertString: PEM-encoded CA certificate string. If provided, this will be used instead of reading from a file.

Example JSON Configuration

"dispatcher": {
    "ca_cert_path": "/path/to/ca.crt",
    
    OR
    
    "ca_cert_string": "-----BEGIN CERTIFICATE-----\n..."
}

Example Environment Variable Configuration

export CONVOY_DISPATCHER_CACERT_PATH=/path/to/ca.crt

OR

export CONVOY_DISPATCHER_CACERT_STRING="-----BEGIN CERTIFICATE-----..."

If both CACertPath and CACertString are provided, CACertString takes precedence.