[Feature request] Add support for OVERRIDE_FIND_PACKAGE

[Jazzinghen]

When adding a package using CPM is not possible to use that package to override the results of find_package, which generates issues with third-party packages using it to find dependencies.

CMake added the option OVERRIDE_FIND_PACKAGE to FetchContent_Declare to help in this case by automatically updating some read-only properties. Would it be possible to support this option?

[Avus-c]

This is already supported :)
All arguments that aren't parsed by CPM directly / CPM doesn't know about, are passed directly to FetchContent_Declare.

Something like this should work.

CPMFindPackage(
  ....
  OVERRIDE_FIND_PACKAGE <name>
  ...
)

[patstew]

It isn't, CPM avoids parts of FetchContent that prevent OVERRIDE_FIND_PACKAGE from working.
This PR fixes it. #604
See also #498