follow-up: automatically detecting missing KEP questions / headings

[BenTheElder]

#5267 created an MVP implementation of this, but it needs some polish and wiring up to CI.

I would suggest only linting newly modified KEPs, old KEPs need not be modified but any actively developed KEP ought to add any missing headings from the KEP template, even if they were not there when the KEP was first authored.

This will help ensure that we don't miss any PRR questions due to outdated KEP template use or unintentional deletion etc.

The few headings which are optional are tagged (Optional) and ignored by the script.

/sig architecture

cc @soltysh @johnbelamaric @pohly @jenshu @kannon92 (some interested parties from the original PR)

I'm a little pressed for time at the moment but I should be able to at least help review ...

[soltysh]

I might find some time, while I'm going through KEPs, b/c this tool is a time saver.

[kannon92]

cc @sohankunkerkar

[soltysh]

I've made some improvements in #5890