Update on Federated Analytics example

[gubertoli]

Issue

Description

This PR proposes a change to the former Federated Analytics example. Previously, the Federated Analytics example was tied to the use of Pandas, and the example's name was quickstart-pandas.

Later changes loaded the Iris dataset with Flower Datasets with the method .with_format("pandas") to keep aligned with the quickstart-pandas.

For a matter of context, I recently had some issues during my search for this Federated Analytics example because of the misleading name as quickstart-pandas.
Then, my PR aims to clear this by keeping the example only within the Federated Analytics scope.

Overall, my understanding is that it is also beneficial for Flower positioning with this clear example showing the framework as applicable for federated analytics applications.

Another example with Pandas (for loading external/custom data not available on Hugging Face and Flower Datasets) can be created as a new quickstart (I can do that).

Related issues/PRs

Initial PR is #1469 and later changed by #2816.

Proposal

Explanation

• updated README.md with a more detailed explanation, and rearranging the sequence of execution steps.
• updated client.py to do not use pandas anymore
• updated requirements.txt and pyproject.toml to remove pandas dependency.
• updated related docs files to keep aligned with the changes

Checklist

• Implement proposed change
• Write tests
• Update documentation
• Update the changelog entry below
• Make CI checks pass
• Ping maintainers on Slack (channel #contributions)

Changelog entry

Any other comments?

N/A