[FEAT] add flag with null value

[Maxtam83]

I intend to configure the provisioning profile to contain a specific value for iOS, but a null value for macOS. (I don’t have the license for macOS). Adding a flag with an empty value is not possible today. It is not possible for me to define the indicator as follows:

"PROVISIONING_PROFILE_SPECIFIER[sdk=macosx*]" = ""

This would avoid having the same value for PROVISIONING_PROFILE_SPECIFIER[sdk=macosx*] and PROVISIONING_PROFILE_SPECIFIER[sdk=macosx*] in my XCode project settings.

project.pbxproj:

isa = XCBuildConfiguration;
			baseConfigurationReference = 3047A50F1AB8059700498E2A /* build-debug.xcconfig */;
			buildSettings = {
				ALWAYS_SEARCH_USER_PATHS = NO;
				ASSETCATALOG_COMPILER_APPICON_NAME = AppIcon;
				CLANG_ENABLE_MODULES = YES;
				CLANG_ENABLE_OBJC_ARC = YES;
				"CODE_SIGN_IDENTITY[sdk=iphoneos*]" = "Apple Development: XXXXX (XXXXXX)";
				CODE_SIGN_STYLE = Manual;
				COPY_PHASE_STRIP = NO;
				"DEVELOPMENT_TEAM[sdk=iphoneos*]" = XXXXXXX;
				FRAMEWORK_SEARCH_PATHS = (
					"$(inherited)",
					"\"TEST APP/Plugins/@thegrizzlylabs/cordova-plugin-genius-scan\"",
					"\"TEST APP/Plugins/@thegrizzlylabs/cordova-plugin-genius-scan\"",
					"\"TEST APP/Plugins/@thegrizzlylabs/cordova-plugin-genius-scan\"",
				);
				GCC_DYNAMIC_NO_PIC = NO;
				GCC_OPTIMIZATION_LEVEL = 0;
				GCC_PRECOMPILE_PREFIX_HEADER = YES;
				GCC_PREFIX_HEADER = "TEST APP/TEST APP-Prefix.pch";
				GCC_THUMB_SUPPORT = NO;
				GCC_VERSION = "";
				INFOPLIST_FILE = "TEST APP/TEST APP-Info.plist";
				IPHONEOS_DEPLOYMENT_TARGET = 11.0;
				LD_RUNPATH_SEARCH_PATHS = "@executable_path/Frameworks";
				PRODUCT_BUNDLE_IDENTIFIER = xx.xxx-xxxxxxx.TEST-IOS;
				PRODUCT_NAME = "$(TARGET_NAME)";
				"PROVISIONING_PROFILE_SPECIFIER[sdk=iphoneos*]" = "iOS Development 2023";
				SUPPORTS_MACCATALYST = YES;
				TARGETED_DEVICE_FAMILY = "1,2";
				VALIDATE_WORKSPACE = NO;
			};
			name = Debug;

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