TypeSpec - Create API review only if main.tsp is present

[praveenkuttappan]

Create API review only if main.tsp is present since API review emitter expects this file. This is to make sure API review is generated at project root level instead of sub product level which still has tspconfig.yml.

So API review task should be triggered at a directory where tspconfig.yml and main.tsp is present.

https://github.com/Azure/azure-rest-api-specs/blob/main/documentation/typespec-structure-guidelines.md#structure

[praveenkuttappan]

This was already completed.