feat: report arbitrary workspace agent session types - #28127

Turns the producers on now that the schema and the write path are in place.

• The agent connects on Agent API 2.11 and reports Stats.session_counts from its normalized map.
• Reconnecting PTY activity is merged into that map rather than overwriting it, since a client is free to label an ssh session reconnecting_pty.
• coder ssh --usage-app passes any app name through instead of rewriting unrecognized ones to ssh.
• The workspace usage API accepts any app_name, normalized at ingestion, so a new IDE needs no Coder change to show up in usage reporting.
• codersdk.AllowedAppNames stays as the deprecated well-known-name list, and the 2.9 and 2.10 client constructors stay for compatibility.

Depends on #28126.