doc: subkey documentation (#9639)

* doc: convert the adoc to md
* add ref to UncheckedExtrinsic
* Add references to the SS58 format
* Add details about the inspect command
* removing command that is no longer available
* reorder display so ss58 representations show up next to each other
* remove deprecated section
* Add doc about the password option
* fix fmt
* minor fixes

fix #6613

Co-authored-by: Kian Paimani <[email protected]>
Co-authored-by: Squirrel <[email protected]>
Co-authored-by: David <[email protected]>