[CMAKE] Better debug install targets

Summary:
The current install-debug behavior installs the same content than the
install-all target (then splits debug from it), which is not
intuitive. This diff renames it to install-all-debug and adds an
install-debug target that matches the install default target
instead.

Depends on D7240.

Test Plan:

ninja install-debug
ninja install-all-debug

Check the output are as expected

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D7243