feat(bridgetown): Add plugin for Ruby bridgetown site generator (#10496)

plugins/bridgetown/README.md

+# Bridgetown plugin
+
+This plugin adds some aliases and autocompletion for common [Bridgetown](https://bridgetownrb.com/) commands.
+
+To use it, add `bridgetown` to the plugins array in your zshrc file:
+
+```zsh
+plugins=(... bridgetown)
+```
+
+## Aliases
+
+| Alias | Command                    |
+|-------|----------------------------|
+| br      | `bridgetown`              |
+| bra     | `bin/bridgetown apply`    |
+| brb     | `bin/bridgetown build`    |
+| brc     | `bin/bridgetown console`  |
+| brclean | `bin/bridgetown clean`    |
+| brd     | `bin/bridgetown deploy`   |
+| brdoc   | `bin/bridgetown doctor`   |
+| brh     | `bin/bridgetown help`     |
+| brn     | `bridgetown new`          |
+| brp     | `bridgetown plugins`      |
+| brpl    | `bridgetown plugins list` |
+| brs     | `bin/bridgetown start`    |

plugins/bridgetown/bridgetown.plugin.zsh

+alias br='bridgetown'
+alias bra='bin/bridgetown apply'
+alias brb='bin/bridgetown build'
+alias brc='bin/bridgetown console'
+alias brclean='bin/bridgetown clean'
+alias brd='bin/bridgetown deploy'
+alias brdoc='bin/bridgetown doctor'
+alias brh='bin/bridgetown help'
+alias brn='bridgetown new'
+alias brp='bridgetown plugins'
+alias brpl='bridgetown plugins list'
+alias brs='bin/bridgetown start'