rapids_cpm_package_override: Always load overrides

[robertmaynard]

Description

rapids-cmake will now always load override entries from disk and populate the internal json state. In the case of CPM_<pkg>_SOURCE this information will still be ignored. This gives advanced users a consistent behavior when calling rapids_cpm_package_details

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[robertmaynard]

@Jacobfaib

[vyasr]

OK I think this makes sense. At first I was concerned that the override would bypass the env var but if we're only doing this for accessing the package metadata then I think it makes sense.

[Jacobfaib]

Minor nit: no need for else() due to continue()

[robertmaynard]

I want the rapids_cpm_${normalized_pkg_name}_override_ignored to exist after any parsing has occured.
This gives us a ternary to determine that parsing has occured plus the outcome.

[Jacobfaib]

No I mean that

if(cond)
  continue()
else()
  foo()
endif()

is identical to

if(cond)
  continue()
endif()
foo()