Leverage PXR_PYTHON_SHEBANG to help with OpenUSD package relocation

[jfpanisset]

From #wg-ci:

Pixar does provide a mechanism to override the default Python shebang and configure it via PXR_PYTHON_SHEBANG, so it could be explicitly set to something more universal like #!/usr/bin/env python3:

https://github.com/PixarAnimationStudios/OpenUSD/blob/dev/CMakeLists.txt#L25-L31

This might help to build a more relocatable OpenUSD Conan package.

[jfpanisset]

The current attempt at remapping paths uses a regex:

aswf-docker/scripts/common/install_conanpackages.sh

Line 116 in 18e4fc0

sed -i -E '1s@^#!/opt/conan_home/d/b/cpyth.*/bin/(.*)$@#!/usr/bin/env \1@' "$f"

but the Conan build cache path seems different in our release builds and the regex fails to match. The Python paths thus remain:

#!/opt/conan_home/d/cpyth0fe0182930756/p/lib/cmake/../../bin/python3.13

The regex needs to be updated to work in both local and release builds, or hopefully we can use PXR_PYTHON_SHEBANG to avoid baking in those Conan cache paths in the first place.