[🚀esl-footnote]: request to have an ability to declare 'reference'/'alt' notes

[ala-n]

As a ESL footnotes consumer, I want to be able to have an ability to have multiple alternative markup presented.

As for now the only option to handle notes clones form the alternative markup is to have them ignored (using breakpoints query for example). But there is no option to have a note presented as an alternative for another note in the content.

Points to consider:

• 'reference' / 'alt' mode for note to be excluded from indexing but reliynig on the defined 'master' node instance (Problem: ability to find a master note)
• consider groping notes with the same content to the same index (was rejected as a main implementation, due to current consumers votes, but possibly we need to renew discussion)