feat: add TroubleJump custom event for autocmds

[nerdo]

This minor change adds a custom TroubleJump event whenever the function is called.

This makes it possible for it to be easily customized to do something like the following to, for example, trigger the floating diagnostic so that one can immediately see more context as one navigates through the jump list:

vim.api.nvim_create_autocmd("User", {
	pattern = "TroubleJump",
	callback = function()
		-- Open the diagnostic float after 300ms.
		vim.schedule(function()
			vim.cmd("lua vim.diagnostic.open_float()")
		end, 300)
	end,
})