CI: Stop building OpenCPN 5.6.2 PI next major update? (near future)

[rgleason]

I propose that we stop building updated versions of plugins for OpenCPN 5.6.2 version at the next major update.

1. Some AP plugins have moved to API118 and will not support O5.6.2 any longer.
2. In the master PIM Catalog we already have a relatively complete set of metadata and tarballs for all the plugins that should work with O5.6.2 Those should be kept intact if at all possible.
3. For the next major update we would add the OpenCPN v5.10 plugins.
4. Should we just keep both the O5.6.2 and O5.8.4 plugin metadata in the catalog? I assume the answer is Yes.
5. However, won't the O5.10 plugins work with O5.8.4 anyway because there is no major wxWidgets change?