Add configuration modifiers to entire directories

Modifiers can be set in PACKAGE files using the prelude's set_cfg_modifiers. In this case they will be applied to all targets affected by that PACKAGE file.

For example, assuming that root//build:debug is an existing constraint value and modifiers have been setup, the following will apply it by default to all targets defined in that PACKAGE's directory:

load("@prelude//cfg/modifier/set_cfg_modifiers.bzl", "set_cfg_modifiers")

set_cfg_modifiers([
    "root//build:debug",
])

set_cfg_modifiers takes 2 arguments:

• cfg_modifiers, a list of modifiers to set.
• extra_cfg_modifiers_per_rule, a dictionary mapping rule names to lists of modifiers that should be applied only for that rule. Note this is deprecated.