action dump-layout: select a specific tab/pane & serialize to JSON

[YPares]

When writing scripts calling zellij action, I often want to extract some information from zellij, for instance:

• what is the layout of the current pane? (is it "alone" in its tab, is it floating, etc.)
• what is the name of the current tab?
• etc.

zellij action dump-layout gives all these information, but it's not convenient to parse from a shell script.

I think two extra features could go a long way:

• add a flag to dump the layout of only a specific pane/tab
• add a flag to serialize the output to json (because jq is kind of omnipresent, and some shells even handle json out of the box, like nushell)