feat(snippets): add option completion.menu.draw.snippet_desc_column

[xieyonn]

The snippet description will be displayed on the document window by default, which is a bit inconvenient.

Generally speaking, snippet description is very short, so I have added an option to display the description directly on the completion menu, in column label_details or label_description.

config example:

opts = {
	completion = {
		menu = {
			draw = {
				snippet_desc_column = "label_description",
			},
		},
	},
}

If snippets provide a description, eg:

snippet desc show desc in menu column
  hello world

Show this description in menu column, see preview:

Already tested for mini_snippets, luasnip, and the default snippets.