feat(kitty): add plugin for the kitty terminal (#10994)

* A plugin for the Kitty terminal

Provides a handful of useful aliases for anyone working in a Kitty
terminal. In particular, the kssh command is handy for ensuring that
terminfo is set correctly on remote hosts when  you ssh to them.

* Guard kitty configuration

We should only load these aliases into a terminal that's identifying
itself as an xterm-kitty terminal. They're not useful in any other
situation.

plugins/kitty/README.md

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+# Kitty plugin
+
+This plugin adds a few aliases and functions that are useful for users of the [Kitty](https://sw.kovidgoyal.net/kitty/) terminal.
+
+To use it, add _kitty_ to the plugins array of your zshrc file:
+```
+plugins=(... kitty)
+```
+
+## Plugin commands
+
+* `kssh`
+  Runs a kitten ssh session that ensures your terminfo settings are copied
+  correctly to the remote hose.
+* `kssh-slow`
+  A slower form of `kssh` that should always work. Use this if `kssh` fails
+  to set terminfo correctly for you on the remote host.
+* `kitty-theme`
+  Browse and change the theme of your Kitty terminal.
+
+## Contributors
+
+- [Ian Chesal](https://github.com/ianchesal)

plugins/kitty/kitty.plugin.zsh

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+#####################################################
+# Kitty plugin for oh-my-zsh                        #
+#####################################################
+
+if [[ "$TERM" == 'xterm-kitty' ]]; then
+  ## kssh
+  # Use this when your terminfo isn't recognized on remote hosts.
+  # See: https://sw.kovidgoyal.net/kitty/faq/#i-get-errors-about-the-terminal-being-unknown-or-opening-the-terminal-failing-when-sshing-into-a-different-computer
+  alias kssh="kitty +kitten ssh"
+  compdef kssh='ssh'
+  # Use this if kssh fails
+  alias kssh-slow="infocmp -a xterm-kitty | ssh myserver tic -x -o \~/.terminfo /dev/stdin"
+
+  # Change the colour theme
+  alias kitty-theme="kitty +kitten themes"
+fi