Add Marketplace datamodel for marketplace.json support (#1744)

Co-authored-by: openhands <openhands@all-hands.dev>

Author: neubig

openhands-sdk/openhands/sdk/plugin/__init__.py

@@ -2,23 +2,38 @@
 
 This module provides support for loading and managing plugins that bundle
 skills, hooks, MCP configurations, agents, and commands together.
+
+It also provides support for plugin marketplaces - directories that list
+available plugins with their metadata and source locations.
 """
 
 from openhands.sdk.plugin.fetch import PluginFetchError
 from openhands.sdk.plugin.plugin import Plugin
 from openhands.sdk.plugin.types import (
     AgentDefinition,
     CommandDefinition,
+    Marketplace,
+    MarketplaceMetadata,
+    MarketplaceOwner,
+    MarketplacePluginEntry,
+    MarketplacePluginSource,
     PluginAuthor,
     PluginManifest,
 )
 
 
 __all__ = [
+    # Plugin classes
     "Plugin",
     "PluginFetchError",
     "PluginManifest",
     "PluginAuthor",
     "AgentDefinition",
     "CommandDefinition",
+    # Marketplace classes
+    "Marketplace",
+    "MarketplaceOwner",
+    "MarketplacePluginEntry",
+    "MarketplacePluginSource",
+    "MarketplaceMetadata",
 ]