Steps to get taxon exclusions from relation graph

[cmungall]

This addresses the relation graph strategy outlined in #2137

[matentzn]

Is this ready to merge? what are the associated steps, i.e. whats next?

[cmungall]

Let's keep this unmerged for now until we have reached more clarity on #2137. If we decide to go a pure TBox strategy then we can close this.

However, I suspect at the least the graph strategy will be a highly useful adjunct to a TBox strategy. In which case we should tidy this PR:

• decide on appropriate file names for products
• which directories they should live in
• how it should be integrated into the main flow

I think for these steps it should be someone more familiar with current ODK idioms that does this work

[github-actions]

This PR has not seen any activity in the past month; if nobody comments or reviews it in the next week, the PR editor will be allowed to proceed with merging without explicit approval, should they wish to do so.