PDI-1459: CLI v2 Command Connector: Platform Export / PingOne (Early access)

[erikostien-pingidentity]

• Add framework and one resource export (pingone_agreement) to pingctl. Further work will follow this adding remaining resources to export subcommand.
• Update test functions to use NewRootCommand() to gain viper functionality in test cases.
• Update most output messages to use Error instead of Fatal to propagate error messages back through the call stack. This is useful for chaining error messages to trace what pingctl was trying to do, as well as make test cases receive stdout for error messaging.
• Update Cobra Run functions to use RunE to allow error propagation as well.
• Update export.go to use PingOne SDK and loop through user-specified services exports. Use user-defined export format and override variables to do so. Default export output directory to pwd. Fail to export if previous export files are present.
• Update ExportableResource to define an ImportBlock struct to house API data and use in text template output to file. Add utility ResourceType function to interface as well.
• Create pingone_platform_connector.go to define a connector for the pingone platform service. Pingone SSO service is to be added in further work.
• Create resources subfolder structure for connectors to define each resource, as well as their sdk-specific logic or exporting data.