Add SpacetimeAuth CLI command

[JulienLavocat]

Description of Changes

TODO:

spacetime auth config

• config set — call the API to persist the setting
• config reset — call the API to reset all config to defaults

spacetime auth idp

• idp set <client_id> <client_secret> — register the OAuth app credentials for the given provider
• idp enable — enable the provider
• idp disable — disable the provider

spacetime auth client

• client create [] — create the client and print the generated client ID/secret
• client delete [] — delete the client
• client get [] [--include-secret] — fetch and display client details; suppress secret unless flag is set
• client set [] — update the given field on the client

API and ABI breaking changes

Expected complexity level and risk

Testing