General: Find executable enhancement

[iLLiCiTiT]

Brief description

Enhance how executables are found when find_executable is called which cause that oiiotools return full path to executable.

Description

Modified function find_executable which can now also fill extension to path to executable if is missing. With this change oiiotools return full path to executable with extension.

Additional information

Proper fix of previous issue from PR #4136 .

Testing notes:

Open Tray > Admin > Console and run this script:

from openpype.lib import get_oiio_tools_path

print(get_oiio_tools_path("oiiotool"))
print(get_oiio_tools_path("maketx"))

Output on windows should return full path to executabls with extensions. It should also still work on linux and mac (if the executables are available there).

[m-u-r-p-h-y]

works as expected