This PR provides :

• Fix for AWS Function Handler name to be in the format of filename.function-name because
  passing paths (what we have now) as function name is giving us import errors from AWS Lambda
• Added the initialisation script for AWS Lambda function handler name to path init_serverless_sdk.sentry_lambda_handler

Current Behavior:
Handler name: sentry_sdk.integrations.init_serverless_sdk.sentry_lambda_handler

Response from AWS

Response
{
  "errorMessage": "Unable to import module 'sentry_sdk.integrations.init_serverless_sdk': No module named 'init_serverless_sdk'",
  "errorType": "Runtime.ImportModuleError",
  "stackTrace": []
}

Note: Unable to replicate in backend tests that actually create real lambda functions and layers. Only able to replicate this behavior on the AWS Console