Add XML documentation for Org.Apache.Http.Impl.Conn

The `Org.Apache.Http.Impl.Conn` namespace contains **498** `To be added` placeholders in source XML documentation (excluding `docs\xml\index.xml`).

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

## Update log

- 2026-09-10: Refreshed the placeholder scan from **497** to **498** (increased by **1**). Related documentation PRs: [#523](https://github.com/dotnet/android-api-docs/pull/523), [#597](https://github.com/dotnet/android-api-docs/pull/597), [#644](https://github.com/dotnet/android-api-docs/pull/644).

Start with the placeholder scan in docs\xml, using the provided rg command and excluding docs\xml\index.xml. Review the files under Org.Apache.Http.Impl.Conn and ns-Org.Apache.Http.Impl.Conn.xml to understand the existing documentation style. Done means replacing the 498 reported “To be added” placeholders with appropriate XML documentation.

Written by the indexing model from the issue text.