Add proxy support (for debugging)

### Your use case

#### What would you like to do?

Add system proxy support to debug builds.

Note: this feature would **not** be available in prod/release builds (see https://github.com/vector-im/element-x-android/issues/328).

#### Why would you like to do it?

So that developers can inspect web traffic, improving developer experience.

Currently, enabling a system wide proxy on Android does not affect the Matrix Rust SDK in Element X Android. This is because applications must pass this setting to their HTTP clients.

#### How would you like to achieve it?

Detect a system wide proxy configured through

```sh
adb shell settings put global http_proxy $PROXY_HOST:$PROXY_PORT
```

Configure the HTTP client with the the proxy URL configured at the system level. Pass the URL the Matrix Rust SDK through APIs introduced in https://github.com/matrix-org/matrix-rust-sdk/pull/2191

### Have you considered any alternatives?

_No response_

### Additional context

_No response_

### Are you willing to provide a PR?

Yes