feature: bedrock agent api support

[martinsafsten]

Issue #, if available: #2007

Description of changes:

I added support for building a .NET Core Web Api with Amazon.Lambda.AspNetCoreServer.Hosting, and use it as a Amazon Bedrock Action Group Lambda Function, configured with a OpenAPI specification. The user simply calls IServiceCollection.AddAWSLambdaHosting(LambdaEventSource.BedrockAgentApi), in the same manner as the existing event sources, which loads up the correct request and response handling.

I have not created a change file. Awaiting a review to see if the general strategy is accepted.

Here is a structured list of the changes:

• Created a new events project for bedrock agent event contracts: Amazon.Lambda.BedrockAgentEvents
• Added new LambdaEventSource in Amazon.Lambda.AspNetCoreServer.Hosting: BedrockAgentApi
• Added request and response marshalling for Amazon Bedrock agents in Amazon.Lambda.AspNetCoreServer when using the new event source.
• Unit tests against the TestWebApi to verify correct marshalling.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.