check data type of the arguments of 'CBA_fnc_addKeybind'

[commy2]

When merged this pull request will:

• @nathan423 was using the function like this:
  ["United Operations", "Admin Console", ["player", [], -10, "_this call uo_fnc_selfInteractMenu", "main"], [DIK_APPS, [false, false, false]], false, "keydown"] call cba_fnc_addKeybind;,
  but the third argument is meant to be a string.
• This is a really nasty error, because that array is stored in the profile and will lead to the following persistent error message:

17:05:28 Error in expression <aram [_forEachIndex, []];

_actionEntry params [["_displayName", "", ["", []]], >
17:05:28   Error position: <params [["_displayName", "", ["", []]], >
17:05:28   Error Params: Type String, expected Array
17:05:28 File x\cba\addons\help\XEH_postClientInit.sqf, line 79

• The only way to remove this error is to clear the keybinding variable from the profile.
• This PR makes it so the function checks the input to prevent errors like this in future.

[PabstMirror]

3rd arg can be array
Throws: Error Params: Type Array, expected String
But just letting it take [] for 3rd arg might not fix the problem with the bad code.

[commy2]

_displayName - Pretty name, or an array of strings for the pretty name and a tool tip [String]

Oh, yeah. Missed that. Will have to do further stuff with this...