cmd/clef: Update README with external v6.0.0 & internal v7.0.1 APIs (#21298)

Changes include:
* Updates response docs for `account_new`, `account_list`, `account_signTransaction`
* Removes `account_import`, `account_export` docs
* Adds `account_version` docs
* Updates request docs for `ui_approveListing`, `ui_approveSignData`, `ui_showInfo`, `ui_showError`, `ui_onApprovedTx`
* Adds `ui_approveNewAccount`, `ui_onInputRequired` docs