Release notes for 0.76 (nushell#770)

* Release notes for `0.76`

Please add your important new features and breaking changes to the release notes by committing to/opening a PR against the `release-notes-0.76` branch. Thank you!

* Add breaking change for plugin signature (nushell#775)

* add breaking change

* Update blog/2023-02-21-nushell_0_76.md

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Co-authored-by: Stefan Holderbach <sholderbach@users.noreply.github.com>

* add some info on debugging commands

* release notes for nushell#7952 (nushell#777)

* release notes for nushell#7952

* Fix html tags that broke CI

* more debug notes

* Add `profile` note and screenshot (nushell#778)

* add ast to debug commands section

* add breaking change (nushell#790)

* Remove example stuff

Don't let the lorem ipsum loose

* added more breaking changes notes

* trim down error message documentation in blog post

* Add description of some commands

* Do some polishing. sequence multiplication

* Screenshot help of a plugin

* Add section on nu plugin

* Add section on background work and full log

* Executive summary

* Details to "mul"

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Co-authored-by: WindSoilder <WindSoilder@outlook.com>
Co-authored-by: Darren Schroeder <343840+fdncred@users.noreply.github.com>
Co-authored-by: Bob Hyman <bob.hyman@gmail.com>
Co-authored-by: Jakub Žádník <kubouch@gmail.com>
Co-authored-by: Reilly Wood <reilly.wood@icloud.com>