feat!: add resession.nvim as backend

[Parsifa1]

this plugins used to help me a lot, but since mksession have a lot of bugs with save fold and it can not works well with https://github.com/tiagovla/scope.nvim, i'd like to offer the https://github.com/stevearc/resession.nvim backend to do the better session save.

it saved as structured json file and more reliable.

this pr should not broken anything ,won't delete the old sessionfile, and those who don't want to using the resession backend will feel nothing.

i know it will became more complicated, so i'm asking what do you think of it.
it's ok if you don't want to merge it because of complexity

if it's ok, i will add some relevant doc later.

[Parsifa1]

maybe useless ...