Add a user_agent_suffix option #1148

JS client parity: tools built on top of the client (integrations, plugins, MCP servers) have no way to identify themselves in the User-Agent header short of replacing the whole header. The Python client builds a fixed User-Agent (_base.py#L161-L166).

The JS client has a userAgentSuffix option (apify_client.ts#L746-L749) that appends one or more parts to the default User-Agent, separated by ; (base.ts#L331-L336).

Add the same option, user_agent_suffix: str | list[str], to ApifyClient, ApifyClientAsync and the built-in HTTP clients, producing the same header format as JS.

✍️ Drafted by Claude Code