Define command completions for fzf_configure_bindings

[PatrickF1]

No description provided.

[PatrickF1]

Todo: consider whether to use two sets of tab completions: 1 for --varariable= (description=change the key sequence for...), 1 for --variable (description=disable the key binding for...).

[PatrickF1]

Decided against it:

• to keep the tab completion menu from getting too packed
• there are almost no examples of completions that include = at the end of the option in fish's official completions
• the = completions don't work well, it still adds a space after selecting the option, suggesting to the user that they can include a space after the option even though it's required