[material-ui] Revamp the free templates design

[zanivan]

This is an umbrella issue for the Material UI templates design revamp.

Objectives

1. Overhaul the existing templates, primarily updating their layouts while preserving the Material Design elements.
2. Remove, merge, or develop new templates as needed.
3. Design a custom theme for the templates, tailoring them to exemplify how-to style Material UI.
4. Make these custom styles readily available for users, preventing disappointments when they attempt to replicate the template's visual in their projects.
5. Use the templates to educate the users on converting the current styling to the zero runtime solution.

Existing templates

First batch

• Album Landing page [material-ui] Replace the Album template with a landing page #37557
• Pricing (Became a section within the landing page template)
• Checkout [material-ui] Refine checkout template #40967
• Sign-in [material-ui] Refine the Sign-in and Sign-up templates #41192
• Sign-in side [material-ui] Refine the Sign-in and Sign-up templates #41192
• Sign up [material-ui] Refine the Sign-in and Sign-up templates #41192

Second batch

• Dashboard [material-ui] Refine Dashboard template #41757
• Blog [material-ui] Refine Blog template #42825
• Sticky footer¹ Wll be removed in [docs] Refine and polish out Templates page #43131

Custom theme

• Unify and standardize the custom themes [material-ui] Refine and unify custom template themes #43220

Further tweaks will be tracked in #41469

Footnotes

1. Will likely be removed from the templates; this makes more sense as a demo or as a “block” in the future ↩

[samuelsycamore]

There's a real nice opportunity for a quick win by adding an MUI X Chart to the Dashboard template! But tbh, that one feels pretty generic to me—seems like we should have several different kinds of dashboards here since that's by far the most common use case.

[mbrookes]

For some historical context, the originals were mostly a blatant rip-off of Bootstrap's free page templates before they introduced paid ones.

This might already be the intention, but with the revamp it would be good if all the pages had a consistent look and feel so that they could theoretically be used together.