(cmake): check CMAKE_BUILD_TYPE value

What does this MR do?

• on Windows, if the user doesn't specify a value for 'CMAKE_BUILD_TYPE', it's automatically initialized to 'Debug' after 'project()' cmake command.
• it's annoying because if we wanted to build in release, we have to clean the cmake cache and define CMAKE_BUILD_TYPE to Release (just redefining CMAKE_BUILD_TYPE isn't enough and is "dangerous")
• so now, we check CMAKE_BUILD_TYPE before cmake command 'project()', and if the user forgets to define CMAKE_BUILD_TYPE before configuring, configuration is stopped and display an error message

How to test it?

• make a cmake configure of Sight without specifying a value for CMAKE_BUILD_TYPE
• configuration is stopped and display an error message

Data

No required data

Additional tests to run

(If you need some specific test e.g Windows compilation...)

• Build on Windows
• Build on Linux
• Build on macOS

Associated issue

Closes #335 (closed)