openapi-to-typespec should not depend on a specific version of typespec

[markcowl]

Because openapi-to-typespec is used by tsp-client, and tsp-client is a dependecy in the specs repo, pinning the version in depenencies acauses multiple versions of typespec to be installed in the azure-rest-api-specs repo.

Ideally openapi-to-typespec would have a more open set of dependencies, similar to the typespec emitters.

This is somewhat urgent, because it has caused problems in two different TypeSpec releases.