Further document --terragrunt-auth-provider-cmd and redo the conten…

…ts. (#3798)

* Further document `--terragrunt-auth-provider-cmd` and redo the contents.

Document the advice in #3769 and fix the contents (add missing sections, reorder to match the text below).

* Update docs/_docs/04_reference/02-cli-options.md

Co-authored-by: Yousif Akbar <11247449+yhakbar@users.noreply.github.com>

* Update docs/_docs/04_reference/02-cli-options.md

Co-authored-by: Yousif Akbar <11247449+yhakbar@users.noreply.github.com>

* Update docs/_docs/04_reference/02-cli-options.md

Co-authored-by: Yousif Akbar <11247449+yhakbar@users.noreply.github.com>

* Update docs/_docs/04_reference/02-cli-options.md

Co-authored-by: Yousif Akbar <11247449+yhakbar@users.noreply.github.com>

* Update docs/_docs/04_reference/02-cli-options.md

Co-authored-by: Yousif Akbar <11247449+yhakbar@users.noreply.github.com>

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Co-authored-by: Yousif Akbar <11247449+yhakbar@users.noreply.github.com>