cmake: enable CMAKE_COLOR_DIAGNOSTICS by default
cmake: enable CMAKE_COLOR_DIAGNOSTICS by default

Related to https://github.com/espressif/esp-idf/issues/4162

Setting this option informs CMake that it should pass
-fcolor-diagnostics flag to the compiler.

(Colorized build system output, like from GNU Make, is produced even
without this flag.)

Note that if the build is done using Ninja and the build output is
redirected (not a TTY), Ninja will still strip the escape codes from
the output. For the case of idf.py, this is handled in the next
commit.

espressif/esp-idf,espressif/esp-idf,espressif/esp-idf,espressif/esp-idf