Documentation appearance improvings

[unbel13ver]

Description of changes

This PR adds two plugins for mdBook package: https://github.com/lambdalisue/rs-mdbook-alerts https://github.com/JorelAli/mdBook-pagetoc

Checklist for things done

• [ ] Summary of the proposed changes in the PR description
• [ ] More detailed description in the commit message(s)
• [ ] Commits are squashed into relevant entities - avoid a lot of minimal dev time commits in the PR
• [ ] Contribution guidelines followed
• [ ] Ghaf documentation updated with the commit - https://tiiuae.github.io/ghaf/
• [ ] PR linked to architecture documentation and requirement(s) (ticket id)
• [ ] Test procedure described (or includes tests). Select one or more:
  • [ ] Tested on Lenovo X1 x86_64
  • [ ] Tested on Jetson Orin NX or AGX aarch64
  • [ ] Tested on Polarfire riscv64
• [ ] Author has run nix flake check --accept-flake-config and it passes
• [ ] All automatic Github Action checks pass - see actions
• [ ] Author has added reviewers and removed PR draft status

Testing

[unbel13ver]

The mdBook-pagetoc plugin files are distributed under the following license:

        DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE 
                    Version 2, December 2004 

 Copyright (C) 2020 Jorel Ali <contact@jorel.dev> 

 Everyone is permitted to copy and distribute verbatim or modified 
 copies of this license document, and changing it is allowed as long 
 as the name is changed. 

            DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE 
   TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION 

  0. You just DO WHAT THE FUCK YOU WANT TO.

@brianmcgillion I wonder how I have to include those files properly in our project?

[humaidq-tii]

The mdBook-pagetoc plugin files are distributed under the following license:

You can reference that license in the package meta field: https://github.com/NixOS/nixpkgs/blob/3c5e005217a71d2521473855cde10bb64332dc0b/lib/licenses.nix#L1262