Allow setting plugin package used in flake

We can use env vars to control use of the
GitHub or WordPress.org plugin build.

Author: john-shaffer

dev/flake.nix

@@ -83,10 +83,11 @@
             else
               builtins.getEnv name);
           phpPackage = getEnv "PHP_PACKAGE" "php";
+          staticDeployPackage = getEnv "STATIC_DEPLOY_PACKAGE" "pluginWpOrg";
           wordpressPackage = getEnv "WORDPRESS_PACKAGE" "default";
           staticDeployLib = inputs.static-deploy.lib.${system};
           staticDeployPkgs = inputs.static-deploy.packages.${system};
-          staticDeploy = staticDeployPkgs.pluginWpOrg;
+          staticDeploy = staticDeployPkgs.${staticDeployPackage};
           # Note that /tmp/xd has to be created to receive traces
           phpOptions = ''
             opcache.interned_strings_buffer = 16