Provide access to JsonSerializerContext via LambdaContext

### Describe the feature

Often your lambda makes API calls, and it would be easier if we via the lambda context could get access to `JsonSerializerContext`

So instead of creating a new instance or a separate source generated JsonSerializerContext could we expose it directly on the `ILambdaContext` where the `JsonSerializerContext` would be initialized?

Or maybe I am missed how your supposed to access the `JsonSerializerContext`

### Use Case

Avoid instantiating multiple JSON serialization contexts.

### Proposed Solution

_No response_

### Other Information

_No response_

### Acknowledgements

- [x] I may be able to implement this feature request
- [ ] This feature might incur a breaking change

### AWS .NET SDK and/or Package version used

Amazon.Lambda.RuntimeSupport 1.8.2
Amazon.Lambda.Core 2.1.0
Amazon.Lambda.Serialization.SystemTextJson 2.3.0

### Targeted .NET Platform

.NET 6

### Operating System and version

NA