userver: CMake Helpers

CMake scripts that are used by the core CMakeLists.txt

It contains several scripts intended for external usage:

• UserverSetupEnvironment.cmake defines userver_setup_environment function that that simplifies userver usage as a submodule of your project:

  userver_setup_environment()

• UserverTestsuite.cmake defines functions for setting up @ref scripts/docs/en/userver/functional_testing.md "testsuite tests":

  userver_testsuite_add_simple()

• UserverGrpcTargets.cmake defines functions for generating userver gRPC clients and services

• AddGoogleTests.cmake defines functions for creating CTest tests from gtest/utest targets

See https://github.com/userver-framework/service_template for an example.