Solution for managing security credentials for 3rd party environments

[ferrisoxide]

Describe the task

Currently we store all security credentials in encrypted files, per Rails' Custom Credentials](https://edgeguides.rubyonrails.org/security.html#custom-credentials) mechanism.

This is fine for our purposes but makes it difficult for other developers to stand up their own version of the tool.

We could move the credentials back out into environment variables, secure them on the server environment where they are used and document the process so other people can stand up their own instances of the application. In any case, we need a process for 3rd parties to be able to deploy their own instances of the application.

NB It might be possible to still use the 'Custom Credentials' approach but move the specific configuration for our instance out of the way for development purposes. In any case, we need to describe a straightforward model for other developers to use.

Success Criteria

• MUST document all required security credentials
• MUST document process for other developers to follow in order to deploy their own instance of the application