[Feature Discussion]: Sorting for tabs

I wanted to open this issue as a discussion about sorting for tabs.

In the following list i have my suggestions for what to do with every sorting option that currently exists. The main issue with defining these for tabs is that a tab can contain multiple buffers.

`insert_after_current`
This would be the same as sorting by `id` (at least with `gt` and `gT`) unless the user has done some custom sorting. Will look into this.

`insert_at_end`
This would be the same as sorting by `id` unless the user has done some custom sorting. Will look into this.

`id`
This is neovim tab handle. And already works.

`extension`
This is hard to define because a tab can contain multiple filetypes. I think it should be disabled this for `tabs`. If the user has a way they want to define this they can always create a custom `sort_by` function.

`relative_directory`
Idem `extention` however it could be possible to define a tabs `directory` as the longest common path between all buffers in the tab.

`directory`
Idem `relative_directory`

`tabs`
This is now vim tabpage number.