[FEATURE] Provide When Clause / Context Key for vim-like navigation in Bookmark List

[alefragnani]

Discussed in #751

^{Originally posted by bkemmer September 19, 2024}
Hi there,
First, thank you for the awesome extension, it is helping me keeping things organized here :-)

Second, I am trying to move to vim biddings and for me it will be useful to keep using the navigation that we have in the autocomplete suggestions, alt+j and alt+k to move between the bookmaks in bookmarks.list.

      {
        "key": "alt+j",
        "command": "bookmarks.<command to go down>", # current arrow down
        "when": "bookmark.list" # is this the right context?
      },
      {
        "key": "alt+k",
        "command": "bookmarks.<command to go up>", # current arrow up
        "when": "bookmark.list" # is this the right context?
      },

Also, it would be interesting deleting a bookmark inside the list, but lets leave this to later.