Only use cert4android when needed (#1802)

* Refactor ClientCertKeyManager and HttpClientBuilder

- Add logging to `ClientCertKeyManager` for better error handling.
- Update `HttpClientBuilder` to conditionally use custom trust manager and hostname verifier based on `allowCustomCerts` flag.
- Rename `customCertsUI` to `allowCustomCerts` in build configuration.

* Update trust manager and hostname verifier selection logic

- Improve logging and error handling in `ClientCertKeyManager`

* App settings: hide certificate settings when custom certificates are not allowed

* Typo