Ccs-digitalmarketplace-apiclient

Add the API client methods for the conversation messages routes

Add new audit types for conversation messages

Allow for use with all currently maintained Python versions:
- 3.9
- 3.10
- 3.11

Note, because request-mock does not support 3.12 yet, neither can we.

Create the ccs-digitalmarketplace-apiclient from the original [digitalmarketplace-apiclient](https://github.com/Crown-Commercial-Service/digitalmarketplace-apiclient/pulls).

For all changes before this version, please see the [digitalmarketplace-apiclient CHANGELOG](https://github.com/Crown-Commercial-Service/digitalmarketplace-apiclient/blob/main/CHANGELOG.md).