migrate openapi-typescript-codegen to openapi-ts

[swaroopar]

openapi-typescript-codegen has announced that it will be deprecated and there is a new project which replaces it - https://github.com/hey-api/openapi-ts

• [ ] Add openapi-ts dependency to npm and generate the client again.
• [ ] Remove openapi-typescript-codegen dependency from package.json
• [ ] Update client generation script
• [ ] update documentation