Add mouse click mappings as default press keymaps

[GCrispino]

It sounds reasonable to me to add a mouse click mapping to the default keymaps for press and press_queue, other than the current defaults of <CR> an <M-CR>, respectively.

For example, adding <2-LeftMouse> (double click) and <M-2-LeftMouse> (double click holding meta key) for press and press_queue, respectively.

This would require changing the following code:

alpha-nvim/lua/alpha.lua

Lines 740 to 743 in de72250

	keymap = vim.tbl_extend("keep", if_nil(vim.tbl_get(config, "opts", "keymap"), {}), {
	press = "<CR>",
	queue_press = "<M-CR>",
	})

to something like this:

 keymap = vim.tbl_extend("keep", if_nil(vim.tbl_get(config, "opts", "keymap"), {}), { 
     press = {"<CR>", "<2-LeftMouse>"}, 
     queue_press = {"<M-CR>", "<M-2-LeftMouse>"}, 
 }) 

Thoughts?