* repo: added 'enable password change' flag (defaults to true for new repositories), which prevents embedding replicas of kopia.repository in pack blobs
* cli: added 'repo change-password' which can change the password of a connected repository
* repo: nit - renamed variables and functions dealing with key derivation
* repo: fixed cache validation HMAC secret to use stored HMAC secret instead of password-derived one
* cli: added test for repo change-password
* repo: negative cases for attempting to change password in an old repository
* Update cli/command_repository_change_password.go
Co-authored-by: Julio Lopez <julio+gh@kasten.io>
Co-authored-by: Julio Lopez <julio+gh@kasten.io>
