Add OSC 52 escape sequence yank

If the `tmux` `set-clipboard` option is set to `on` add the `osc52yank`
plugin and change `<leader>y` mapping to use it.

vimrc

@@ -199,3 +199,10 @@ Pack 'mustache/vim-mustache-handlebars'
 Pack 'joshglendenning/vim-caddyfile'
 Pack 'kbenzie/vim-khr'
 Pack 'jrozner/vim-antlr'
+
+" Plugins for remote integrations
+Pack 'greymd/oscyank.vim', {'type': 'opt'}
+let g:use_osc52 = trim(system('tmux show-options -g set-clipboard')) ==# 'set-clipboard on'
+if g:use_osc52
+  packadd oscyank.vim
+endif