Update VMAccess README - Githubissues

The README contains the following changes:

Update documentation on using VMAccess with Azure CLI and Powershell (remove outdated documentation regarding ASM)
Added information on using restore_backup_ssh and remove_prior_keys in protected settings
Update public settings with disk_name attribute (has been implemented for a while)
Include documentation for using ED25519 SSH keys
Fixed broken/outdated hyperlinks

Azure / azure-linux-extensions