The new Client classes are thin wrappers around an httpx AsyncClient,
allowing us to perform asynchronous requests in an event loop context.
Moreover, they model the argument and return types of all calls with the
same model classes that are used for the server, ensuring client and
server content exchange is compatible.

The base Client class does all the main logic of parsing/serialising
arguments and responses, and building URLs for the target host/port. On
top of that a StandaloneClient class starts its own TMLite server on the
background using uvicorn.

Documentation for public functions has been added to the autogenerated
API docs page.

This work is part of YAN-950

.

Signed-off-by: Rodrigo Tobar <rtobar@icrar.org>