Fixing indentation in the generated configuration (#1663) (#1668)

- Cherry Picking #1663. 

----------------

## Why make this change?

- With the overhaul of the config system using our own Write method
while serializing objects, the config that is generated is misaligned
with respect to indentation for all the keys under each entity name. For
e.g.:
In the following picture, the entity name `Todo` is indented with 4
leading spaces, subsequently its child key `source` should have been
indented with 6 leading spaces, however its currently indented with only
2 spaces.



![image](https://github.com/Azure/data-api-builder/assets/3513779/4c4a926f-ae22-444e-bc86-23f207b3cf22)

- This is a regression in 0.8.44-rc.

## What is this change?

- Use the same writer to serialize the subkeys under the entity name so
that the depth of indentation is maintained.

## How does this change fix the issue?
- `WriteRawValue` writes the json string argument provided as is without
doing any additional formatting on it. It doesn't utilize the
`_currentDepth` private member of the writer to determine how to indent.

- Prior to this change, we were generating the inner json string first
then writing the generated inner json "as is". While generating that
json on line 29



https://github.com/Azure/data-api-builder/blob/31b754251832ffebf4c4ce36ffcbead9baff6355/src/Config/Converters/RuntimeEntitiesConverter.cs#L29

Line 29 in

[31b7542](31b7542)

a new writer is being used by the `JsonSerializer.Serialize()` function,
effectively resetting the `_currentDepth`. The `_currentDepth` of the
writer in context was not getting honored.

## How was this tested?

- Manual test, building solution and using `dab add` to simulate
automatic writing of an entity to the config file. With the change, the
indentation is fixed.



![image](https://github.com/Azure/data-api-builder/assets/3513779/bf708ecc-4fa2-4711-ba88-844c24922b81)

Author: Aniruddh25

src/Config/Converters/RuntimeEntitiesConverter.cs

@@ -26,9 +26,8 @@ public override void Write(Utf8JsonWriter writer, RuntimeEntities value, JsonSer
         writer.WriteStartObject();
         foreach ((string key, Entity entity) in value.Entities)
         {
-            string json = JsonSerializer.Serialize(entity, options);
             writer.WritePropertyName(key);
-            writer.WriteRawValue(json);
+            JsonSerializer.Serialize(writer, entity, options);
         }
 
         writer.WriteEndObject();