[feat] Carry over tags when splitting

[ekamil]

This is a feature request :D When splitting a note by headers the tags currently attached to the parent note should be carried over. Optionally:

• copy the whole of frontmatter
• allow to use {{tags}} placeholder in note template

I think this is kinda connected to #59 - theme of preserving metadata.

[Fred-Vatin]

I suggest an option named frontmatter template where one could list the keys they want to be copied.