[DashboardLayout] Improve header title customizability

[apedroferreira]

Summary

Right now, customization options for the title that shows in the layout header are quite limited.
Even though it might be possible to do it by using the sx prop in DashboardLayout and targeting the correct element, we could find ways to make that title more straightforward to customize, as it might be something many users want more control over.

A simple, flexible solution might just be adding a new slot for that title.

Examples

No response

Motivation

User feedback on docs: "How to style the branding title? Can I change it to a component instead of a text?"

Search keywords: dashboard layout header branding title appbar style