Make the shotgrid_login package installable in Open RV

[chxmberland]

Fixes #492

Summarize your change.

In this pull request, adjustments have been made to the rv_stage CMAKE macro. This change allows for the flexible inclusion of external directories in .rvpkg files during build time using an INCLUDE_DIR parameter.

The changes use the CMAKE_CURRENT_BINARY_DIR to copy and merge the existing .rvpkg zip file with an external directory requested by the user.

Describe the reason for the change.

With this change, the sgtk dependency can be easily included with the shotgrid_login package during build time through the RV_STAGE macro. Including the sgtk dependency in the shotgrid_login prevents the console build error described in issue #492.

Describe what you have tested and on which operating system.

All tests have been conducted manually on macOS Sonoma 14.5.

Add a list of changes, and note any that might need special attention during the review.

• [ ] Add INCLUDE_DIR parameter to RV_STAGE macro
• [ ] Add additional build step when INCLUDE_DIR parameter is included where the specified directory is merged with the existing package using the CMAKE_CURRENT_BINARY_DIR

If possible, provide screenshots.

[chxmberland]

Changes discarded for a better solution directly in the shotgrid_login package.