Add XML documentation for Org.Apache.Http.Conn

The `Org.Apache.Http.Conn` namespace contains **64** `To be added` placeholders in source XML documentation (excluding `docs\xml\index.xml`).

```powershell
rg -n -i --glob 'Org.Apache.Http.Conn/**' --glob 'ns-Org.Apache.Http.Conn.xml' 'to be added' docs\xml
```

## Update log

- 2026-09-10: Refreshed the placeholder scan from **88** to **64** (reduced by **24**). Related documentation PRs: [#522](https://github.com/dotnet/android-api-docs/pull/522), [#644](https://github.com/dotnet/android-api-docs/pull/644).

Run the provided rg command against docs\xml to list the 64 remaining placeholders under Org.Apache.Http.Conn and ns-Org.Apache.Http.Conn.xml. Read the surrounding API entries and the related documentation PRs for context. Done means replacing the namespace's applicable “To be added” entries with documentation and confirming the scan no longer finds them.

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