Merged PR 348: #2462 - Refactor of DatabaseClient and DatabaseServer

## Summary
Refactor of `DatabaseClient` and `DatabaseService` to update how connection IDs are generated. These are now provided by DatabaseService when establishing a connection.
Creation of `DatabaseClientConnection` class. This is used by `DatabaseClient` to hold a dictionary of active db connections.

## Test process
Tests have been updated to reflect the changes and all pass

## Checklist
- [X] PR is linked to a **work item**
- [X] **acceptance criteria** of linked ticket are met
- [X] performed **self-review** of the code
- [X] written **tests** for any new functionality added with this PR
- [X] updated the **documentation** if this PR changes or adds functionality
- [ ] written/updated **design docs** if this PR implements new functionality
- [X] updated the **change log**
- [X] ran **pre-commit** checks for code style
- [X] attended to any **TO-DOs** left in the code

Related work items: #2462

docs/source/simulation_components/system/applications/database_client.rst

@@ -14,13 +14,14 @@ Key features
 
 - Connects to the :ref:`DatabaseService` via the ``SoftwareManager``.
 - Handles connecting and disconnecting.
+- Handles multiple connections using a dictionary, mapped to connection UIDs
 - Executes SQL queries and retrieves result sets.
 
 Usage
 =====
 
 - Initialise with server IP address and optional password.
-- Connect to the :ref:`DatabaseService` with ``connect``.
+- Connect to the :ref:`DatabaseService` with ``get_new_connection``.
 - Retrieve results in a dictionary.
 - Disconnect when finished.
 
@@ -28,6 +29,7 @@ Implementation
 ==============
 
 - Leverages ``SoftwareManager`` for sending payloads over the network.
+- Active sessions are held as ``DatabaseClientConnection`` objects in a dictionary.
 - Connect and disconnect methods manage sessions.
 - Payloads serialised as dictionaries for transmission.
 - Extends base Application class.
@@ -63,6 +65,9 @@ Python
     database_client.configure(server_ip_address=IPv4Address("192.168.0.1"))  # address of the DatabaseService
     database_client.run()
 
+    # Establish a new connection
+    database_client.get_new_connection()
+
 
 Via Configuration
 """""""""""""""""