Beta lane hardcodes configuration: "Beta", preventing customization

[ssestak]

Problem

The beta lane hardcodes configuration: "Beta" in build_ios_app, which overrides any configuration set via ENV["ADDITIONAL_BUILD_SETTINGS"]:

build_ios_app(build_settings.merge({
  configuration: "Beta"
}))

The .merge() overwrites any configuration key from ADDITIONAL_BUILD_SETTINGS, forcing projects to override the entire lane to use a different build configuration.

Suggested fix

Allow override via ENV while keeping "Beta" as default:

build_ios_app(build_settings.merge({
  configuration: ENV["BETA_CONFIGURATION"] || "Beta"
}))

Or let build_settings (which respects ADDITIONAL_BUILD_SETTINGS) be the source of truth by only setting configuration if not already present.

Migrated from futuredapp/fastlane#213