Support mTLS

### 🔖 Enhancement description

I would like to be able to specify an SSL Socket Factory on the OkHttpClient.Builder when I'm creating a Client so that I can support mutual TLS for a self-hosted instance that's behind a proxy.

Essentially, add a method like:

```
fun sslSocketFactory(
sslSocketFactory: SSLSocketFactory,
trustManager: X509TrustManager
): Client {
http = http.newBuilder().sslSocketFactory(sslSocketFactory, trustManager).build()
return this
}
```

### 🎤 Pitch

For self-hosted instances, there are a variety of common practices to increase security by reducing the exposure to the public internet. Two common practices are using a VPN and using mutual TLS behind a proxy. This lets apps guard access to the server by client certificates which can be issued and revoked individually, improving security to access the instance.

### 👀 Have you spent some time to check if this issue has been raised before?

- [x] I checked and didn't find similar issue

### 🏢 Have you read the Code of Conduct?

- [x] I have read the [Code of Conduct](https://github.com/appwrite/.github/blob/main/CODE_OF_CONDUCT.md)