FindImageMagick: Update documentation

- Synced module documentation with other similar find modules.
- Removed CMake 2.8.8 version info as these are now being cleaned from
  the CMake 4 documentation.
- Added some additional versionadded directives for those items that
  were added after the CMake 3.0.0 module state.
- Added separate components section.
- Reworded few descriptions.
1 file changed