Restructure Release Notes (#5832)

* 1st try at restructuring

* Add emojis and do-not-miss section

* Apply suggestions from code review

Co-authored-by: Michael Osthege <michael.osthege@outlook.com>
Co-authored-by: Ricardo Vieira <28983449+ricardoV94@users.noreply.github.com>

* Improve structure based on review

* Apply suggestions from code review

Co-authored-by: Ricardo Vieira <28983449+ricardoV94@users.noreply.github.com>

* Improve structure again

* Add release announcement

* Apply suggestions from code review

Co-authored-by: Thomas Wiecki <thomas.wiecki@gmail.com>

* Apply suggestions from code review

Co-authored-by: Thomas Wiecki <thomas.wiecki@gmail.com>

* Apply suggestions from code review

Co-authored-by: Thomas Wiecki <thomas.wiecki@gmail.com>

* Add highlight of JAX backend.

* Remove BART section and move links to where we remove it.

* Move BART further down. Remove mention of size.

Co-authored-by: Michael Osthege <michael.osthege@outlook.com>
Co-authored-by: Ricardo Vieira <28983449+ricardoV94@users.noreply.github.com>
Co-authored-by: Thomas Wiecki <thomas.wiecki@gmail.com>

Author: 4 people