Export Kealib CMake package with Kealib::Kealib

[dg0yt]

For #31 (comment):

Enable the following usage pattern:

find_package(Kealib CONFIG REQUIRED)
target_link_libraries(main PRIVATE Kealib::Kealib)

• Independent of Kealib library linkage.
• Package name consist with project name.
• Target name and namespace consistent with package name.

Enable the following usage pattern (untested):

add_subdirectory(my-kealib-subdir)
target_link_libraries(main PRIVATE Kealib::Kealib)

[gillins]

@petebunting any objections to this?

[petebunting]

I have no objections.

[gillins]

Confirmed not to break GDAL 3.8.1.