#2257: rearrange software pages + creating a list of applications and services which is hopefully a single point that should be referred to

docs/source/simulation_components/system/services/dns_client.rst

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+.. only:: comment
+
+    © Crown-owned copyright 2023, Defence Science and Technology Laboratory UK
+
+DNSClient
+=========
+
+The DNSClient provides a client interface for connecting to the ``DNSServer``.
+
+Key features
+^^^^^^^^^^^^
+
+- Connects to the ``DNSServer`` via the ``SoftwareManager``.
+- Executes DNS lookup requests and keeps a cache of known domain name IP addresses.
+- Handles connection to DNSServer and querying for domain name IP addresses.
+
+Usage
+^^^^^
+
+- Install on a Node via the ``SoftwareManager`` to start the database service.
+- Service runs on TCP port 53 by default. (TODO: TCP for now, should be UDP in future)
+- Execute domain name checks with ``check_domain_exists``.
+- ``DNSClient`` will automatically add the IP Address of the domain into its cache
+
+Implementation
+^^^^^^^^^^^^^^
+
+- Leverages ``SoftwareManager`` for sending payloads over the network.
+- Provides easy interface for Nodes to find IP addresses via domain names.
+- Extends base Service class.