Release notes for 0.103.0 (#1783)

* Release notes for `0.103.0`

Please add your new features and breaking changes to the release notes
by opening PRs against the `release-notes-0.103.0` branch.

## TODO
- [ ] look at interesting contributions
- [ ] write all the sections
- [ ] order the sections by interest
- [ ] add the breaking changes
- [ ] detail the breaking changes
- [ ] add the full changelog
- [ ] complete all the `TODO`s inside the release note
- [ ] ... (PRs that need to land before the release, e.g. [deprecations](https://github.com/nushell/nushell/labels/deprecation) or [removals](https://github.com/nushell/nushell/pulls?q=is%3Apr+is%3Aopen+label%3Aremoval-after-deprecation))

* Include link to plugins in 0.103 release notes (#1789)

* Fix date on 0.103 release notes

* Move file

* Add full changelog to date

* Categorize PRs

* Release note addition for 'to yal' (#1828)

* Fix tables

* Write removals section

* Write the additions section

* Fix typo

* Update full changelog and other notes

* Add std-rfc description

* Add writeup for Background Jobs

* Add experimental statement for background jobs

* Add writeup for backtrace, banner theme, `str expand` padding

* Add breaking change descriptions

* Custom command attributes writeup

* Added vi-mode enhancements, new official packages, LSP/Completions from BlindFS

* Added excerpt

* Wordsmithing

* Link to custom command attrs highlight

* Add TOC, update changelog

---------

Co-authored-by: NotTheDr01ds <[email protected]>
Co-authored-by: Ian Manske <[email protected]>
Co-authored-by: Loïc Riegel <[email protected]>

Author: 4 people