I have successfully got the updated version of apcupsd with the new libgd.so.3 link installed.
What I did was uninstall apcupsd first.
Then I renamed the file in the cache from apcupsd-3.14.14-7.ipfire to apcupsd-3.14.14-7.old
This has to be done after uninstalling. If you do it before then uninstalling will place the same version in the cache so that you don’t have to download if it is the same version that you are installing. In you case it will be the sarg cache file you will need to rename. Choose the most recent version of it as there might be multiple copies.
Then after renaming the cache file install sarg again and as there is no cache version of the file a new copy will be downloaded and then installed. It should then work.
Certainly my apcupsd upsimage.cgi page is now showing all the images and the linked lib file is the correct libgd.so.3
After successfully getting everything installed again you will be able to delete the .old version as a correct version will now be in the cache.