feat(framework:cli): Add MLX template for `flwr new`

[charlesbvll]

Issue

Description

We have no template for MLX when using flwr new.

Related issues/PRs

N/A

Proposal

Explanation

Add a new template that create a MLX project.

Checklist

• [x] Implement proposed change
• [x] Update the changelog entry below
• [x] Make CI checks pass
• [x] Ping maintainers on Slack (channel #contributions)

Changelog entry

Any other comments?

N/A