Extend imports for new types/kinds

[Duncan McGreggor]

Tasks:

• Change import --type to --format
• Add support for --type (kind)
• Add JSON deserialisation capability
• Add json to the allowed types for import
• If the --type for import is Kind::AsymmetricCrypto, Kind::Certificates, or Kind::ServiceCredentials, set the format to JSON
• If no type is set, check the file extension
• When exporting to JSON, support limiting by --category
• When exporting to JSON, support limiting by --tags

Depends on:

• #71