Reject conflicting DNS flags (#1559)

Rejects conflicting DNS configuration when `--no-dns` is supplied
together with explicit DNS flags.

Fixes #1536.

Sources/Services/ContainerAPIService/Client/Flags.swift

@@ -344,6 +344,21 @@ public struct Flags {
 
         @Option(name: [.customLong("volume"), .short], help: "Bind mount a volume into the container")
         public var volumes: [String] = []
+
+        public func validate() throws {
+            if dnsDisabled {
+                let hasDNSConfig =
+                    !dns.nameservers.isEmpty
+                    || dns.domain != nil
+                    || !dns.options.isEmpty
+                    || !dns.searchDomains.isEmpty
+                if hasDNSConfig {
+                    throw ValidationError(
+                        "`--no-dns` cannot be used with DNS configuration flags (`--dns`, `--dns-domain`, `--dns-option`, `--dns-search`)"
+                    )
+                }
+            }
+        }
     }
 
     public struct Progress: ParsableArguments {