Add client for interacting with the public dataset registry

[fordN]

This PR adds a registry client for interacting with the public registry.

Supported functionality:

• list()
• search()
• ai_search()
• get()
• list_versions()
• get_version()
• get_manifest()
• publish()
• publish_version()
• update()
• update_visibility()
• update_version_status()
• delete_version()

Example usage:

client = RegistryClient()
results = client.datasets.search('ethereum blocks')
for dataset in results.datasets:
      print(f"[{dataset.score}{dataset.namespace}/{dataset.name}")