Add readonly archives

Problem
For Capella there is a need to allow uses to download the backup taken. This is to allows users to have control over their own data and to support user drive backup strategies. Such as 3,2,1 and off siting the backups.

To limit the surface areas of the downloadable backups, we want to limit them to only be able to run the following subcommands:

• restore
• info
• list

Meaning compaction, backup and merge will not work.

Suggestion
In the archive .backup file, a new field is added called read_only which takes a Boolean. This will be set my Capella when creating the downloadable backup.