chore: update botocore model

[wangyb-A]

Description

• Update sdk model file path from parent folder to src folder
• Add a lambda client initialization test case
• Update boto model json with the full file instead of DEX ones

Testing

1. hatch build
2. install the .whl file to venv
3. test with:

    endpoint = "https://durable.durable-functions.devo.us-west-2.lambda.aws.a2z.com"
    region = "us-west-2"

    client = LambdaClient.initialize_from_endpoint_and_region(endpoint, region)
    client.checkpoint(durable_execution_arn="dummy", checkpoint_token="dummy", updates=[], client_token=None)
    client.get_execution_state(durable_execution_arn="dummy", checkpoint_token="dummy", next_marker="xx")

[wangyb-A]

I will test the boto change after the change is sync to gitfarm with local runner

[wangyb-A]

We will remove the preview model later so not harmful to add the whole json model file. Also make it easier to sync with any new API changes.

[yaythomas]