Add Local Config for ngrok URLs to prevent CONFIG.js conflicts during development

[Jag96]

Problem

Currently, if we want to update CONFIG.js, the diff from the ngrok changes is included, and you have to work around that when managing git diffs.

Solution

Keep the ngrok URLs in a local config, and gitignore that config, so this doesn't keep happening. Additionally, we'll need to update the readme so developers will update their local config instead of the current config

[tgolen]

Would it be possible to handle the local config stuff like I'm doing here in the webpack config for the report IDs? https://github.com/AndrewGable/ReactNativeChat/pull/133/files#diff-f829eca9ad810a385b046aa894f64f1eR16

[Jag96]

Yeah, it looks like that'd work! We'd just need to add a value for API_ROOT and AUTH_URL in both the production/dev webpack configs, and then remove the IS_IN_PRODUCTION check for those.

[Jag96]

Fixed by #283