[2nd generation] Support optional keyword and other terraform 1.3 language enhancements

[mrlexor]

Hello,

I've found out this closed issue regarding optional modifier. It's actually work, but not as expected.

Optional modifier has two arguments and if I use it only with as shown one, so linter shows that okay:

However, when I add the second one, default argument, linter, seems, doesn't know about it:

Can you take a look, please?

Here you may find information about default argument for the optional modifier.

Originally posted by @mrlexor in #338 (comment)