add charon exit and restructure for clarity (#504)

* add charon exit and restructure for clarity

* update single validator commands

* update nimbus

* Exit command improvements (#520)

* Update quickstart-exit.mdx

* changes from review

* Update quickstart-exit.mdx

fixing "threshold" language

* Update quickstart-exit.mdx

minor typo fixes

---------

Co-authored-by: Kaloyan Tanev <24719519+KaloyanTanev@users.noreply.github.com>
Co-authored-by: Max Sherwood <63233138+slugmann321@users.noreply.github.com>