feat(builtin.buffers): enhance and bind delete_buffer action (#3145)

* feat(builtin.buffers): enhance and bind `delete_buffer` action

* change default bind and add docs

* [docgen] Update doc/telescope.txt
skip-checks: true

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Co-authored-by: Github Actions <actions@github>

lua/telescope/builtin/__internal.lua

@@ -972,6 +972,9 @@ internal.buffers = function(opts)
       previewer = conf.grep_previewer(opts),
       sorter = conf.generic_sorter(opts),
       default_selection_index = default_selection_idx,
+      attach_mappings = function(_, map)
+        map({ "i", "n" }, "<M-d>", actions.delete_buffer)
+      end,
     })
     :find()
 end