Add env variable to set path prefix (#706)

* Add env variable to set path prefix

- When routing traffic to our new URL, the path prefix needs to be blank
- adding path prefix to be set by env var to yml files

* Update reference to env var in PATH_PREFIX

* Update PR message URL with CDN

- The actual website will point to the base url CDN

client/gatsby-config.js

@@ -7,7 +7,7 @@ module.exports = {
     title: 'Justice40',
     image: '/static/favicon.ico',
   },
-  pathPrefix: `/justice40-tool/${process.env.DESTINATION_FOLDER}`,
+  pathPrefix: `${process.env.PATH_PREFIX}`,
   plugins: [
     {
       resolve: 'gatsby-plugin-sass',