docs(framework) Update how to upgrade to Flower 1.13 documentation

[dstripelis]

• Added server and client app examples for versions 1.11+.
• Moved sentence highlighting to latest flower versions.

[chongshenng]

@dstripelis Thanks for starting this update! There're 2 large parts that need to be updated:

• On the Deployment Engine, we no longer use flower-server-app and flower-client-app. These need to be removed. Maybe you can work together with @Robert-Steiner since he has PR docs(framework) Add how-to run flwr with deployment engine guide #4372 which also updates the deployment engine mode. The secure connection part also needs to be updated (e.g. by referring to doc/source/docker/enable-tls.rst in docs(framework:skip) Update Docker docs for 1.13.0 #4470).
• On the Simulation Engine, let's update to the latest server_fn and client_fn usage. We should start either modes by using flwr run, and keep run_simulation for running in notebooks (less use and emphasized).

[jafermarq]

Should we also remove the requirements.txt comment at the top of the document as well as the "Using Poetry" section? Although people can choose to use them, neither of those will work in a deployment setup that relies on the FAB-delivery mechanism. Because of this I think it's better to remove them.

Another point, I'm wondering if it would be better to split the code blocks for ClientApp, ServerApp, Simulation CLI and Simulation Notebook into several (one for current method, other for before 1.1x.0, other for the super legacy method). I think that way would be easier to spot the differences.

[dstripelis]

@jafermarq thank you for the insightful feedback. In the latest commit I addressed all comments except for splitting the code blocks for ClientApp, ServerApp, Simulation CLI and Simulation Notebook into several ones. We should do this in the next release since there are many pieces that need to be moved around in order to support this. In the future, we could even have entirely different doc pages for different versions, e.g., <>/1.13/how-to-upgrade-to-flower-next.html , <>/1.14/how-to-upgrade-to-flower-next.html.

Overall the latest commit does the following:

• Remove using pip header
• Remove using Poetry header AND section
• Added ellipsis in place of partitions
• Removed pyproject.toml config from simulation
• Added tip suggestion in both CLI and notebook simulations

Obsolete