fourth hanging_indent_style to match air?

[myoung3]

This is my air.toml file:

[format]
line-width = 87
indent-width = 2
indent-style = "space"
line-ending = "auto"
persistent-line-breaks = true
exclude = []
default-exclude = true
skip = []
table = []
default-table = false

Here is some code formatted by air with the above air.toml settings:

dt[,
  var := (var1 |
    var2 |
    var3)
]

running lintr::lint on this code returns an indentation_linter error regardless of the value of hanging_indent_style ("always" "never" and "tidy") with the default indent of 2.

Documenting this example for future reference. Once air is more stable, I think it would be good to implement a fourth hanging_indent_style that matches air.