Bitcoin node container will not work for versions other than v29

[edilmedeiros]

Follow up of #3: I realized that we added an argument to enable fetching and compiling versions other than v29 of bitcoin core. But we only included cmake build commands, which only work for v29 and after.

[0xB10C]

At least for peer-observer, only v28 and v29 are fully supported anyway. Before that, not all tracepoint PRs were merged and I was running custom patches.

[edilmedeiros]

So, probably best would be to add a check to not allow anything before v29 and consider it a day.