Here is a new version of this patch. I have been working together with Ashutosh on this. While the version 0 was more of a fragile demo, this version 1 has a fairly complete minimal feature set and should be useful for playing around with. We do have a long list of various internal bits that still need to be fixed or revised or looked at again, so there is by no means a claim that everything is completed.
PFA the patchset fixing compilation error reported by CI bot.
0001 - same as previous one
0002 - fixes compilation error
0003 - adds support for WHERE clause in graph pattern missing in the first patch.