fix: Add DNS server configuration support for internal hostname resolution

Added dns_servers variable to allow configuring custom DNS servers for
the container to resolve internal hostnames.

Changes:
- Added dns_servers variable (list of strings, default empty)
- Added dns configuration to docker_container resource in main.tf
- Allows container to resolve internal domains like gitea.bsdserver.nl

This fixes the ENOTFOUND DNS resolution error where the container
couldn't resolve internal Gitea hostname, which was being reported
as an "Authentication failure" but was actually a network/DNS issue.

The error was:
  getaddrinfo ENOTFOUND gitea.bsdserver.nl

Usage:
  dns_servers = ["192.168.x.x", "192.168.x.y"]

If not specified (default), container uses Docker's default DNS.

main.tf

@@ -49,6 +49,9 @@ resource "docker_container" "renovate" {
     name = data.docker_network.traefik_network.name
   }
 
+  # DNS configuration for internal hostname resolution
+  dns = var.dns_servers
+
   # Volumes
   volumes {
     volume_name    = docker_volume.renovate_config.name

variables.tf

@@ -51,6 +51,12 @@ variable "create_cname_record" {
   default     = false
 }
 
+variable "dns_servers" {
+  description = "List of DNS servers for the container to use for hostname resolution"
+  type        = list(string)
+  default     = []
+}
+
 # Renovate Platform Configuration
 
 variable "renovate_autodiscover" {