Add `new_from_inner()` to `FlightSqlServiceClient`

**Is your feature request related to a problem or challenge? Please describe what you are trying to do.**

Since `FlightSqlServiceClient` does not provide a constructor function with a `FlightServiceClient`, I cannot configure the `FlightServiceClient`, such as setting `max_decoding_message_size`. Providing `inner_mut()` is not enough, since `FlightServiceClient` only supports configuration through the builder functions. Consequently, I cannot use `FlightSqlServiceClient`.

**Describe the solution you'd like**

Add a constructor function `new_from_inner()` like this:

```rust
pub fn new_from_inner(flight_client: FlightServiceClient) -> Self {
Self {
token: None,
headers: HashMap::default(),
flight_client
}
}
```

**Describe alternatives you've considered**

None.

**Additional context**

None.

Start at the FlightSqlServiceClient implementation and inspect how its FlightServiceClient is currently constructed. Add the requested new_from_inner() entry point and verify that the project builds and the client behavior remains covered by the relevant tests.

Written by the indexing model from the issue text.