CI: fixed architecture

Summary

This MR aims at unifying architecture on the different platforms, now everything is done under ~/builds/otb regardless of the namespace or the project.

Future work

A switch can be implemented in the CMake scripts so that local build using CI scripts will not pollute the source dir.

Copyright

The copyright owner is CNES and has signed the ORFEO ToolBox Contributor License Agreement.

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Check before merging:

• All discussions are resolved
• At least 2 votes from core developers, no vote.
• The feature branch is (reasonably) up-to-date with the base branch
• Dashboard is green
• Copyright owner has signed the ORFEO ToolBox Contributor License Agreement
• Optionally, run git diff develop... -U0 --no-color | clang-format-diff.py -p1 -i on latest changes and commit