Create fish_[default|vi]_key_bindings documentation

- Create docs file for both vi and default key bindings
- Remove variable mention on `interactive` and point to their own pages

(cherry picked from commit 564039093b)

doc_src/cmds/fish_default_key_bindings.rst

@@ -0,0 +1,27 @@
+.. _cmd-fish_default_key_bindings:
+
+fish_default_key_bindings - set emacs key bindings for fish
+===============================================================
+
+Synopsis
+--------
+
+.. synopsis::
+
+    fish_default_key_bindings
+
+Description
+-----------
+
+``fish_default_key_bindings`` sets the emacs key bindings for ``fish`` shell.
+
+Some of the Emacs key bindings are defined :ref:`here <emacs-mode>`.
+
+There are no parameters for ``fish_default_key_bindings``.
+
+Examples
+--------
+
+To start using vi key bindings::
+
+  fish_default_key_bindings

doc_src/cmds/fish_vi_key_bindings.rst

@@ -0,0 +1,36 @@
+.. _cmd-fish_vi_key_bindings:
+
+fish_vi_key_bindings - set vi key bindings for fish
+===============================================================
+
+Synopsis
+--------
+
+.. synopsis::
+
+    fish_vi_key_bindings
+    fish_vi_key_bindings [--no-erase] [INIT_MODE]
+
+Description
+-----------
+
+``fish_vi_key_bindings`` sets the vi key bindings for ``fish`` shell.
+
+If a valid *INIT_MODE* is provided (insert, default, visual), then that mode will become the default
+. If no *INIT_MODE* is given, the mode defaults to insert mode.
+
+The following parameters are available:
+
+**--no-erase**
+    Does not clear previous set bindings
+
+Further information on how to use :ref:`vi-mode <vi-mode>`.
+
+Examples
+--------
+
+To start using vi key bindings::
+
+  fish_vi_key_bindings
+
+or ``set -g fish_key_bindings fish_vi_key_bindings`` in :ref:`config.fish <configuration>`.