feat(config): Rework how we grab the mfe_config based on domain cha…

[becdavid]

…nge.

With a S3/Cloudfront distribution fro the MFE frontends, we went with a https://{mfe}.{lms-domain} change making the MFE app a subdomain of the lms domain.

Example of additional BASE_URL needed within each MFE app configuraiton.

{
    "MFE_CONFIG": {
        "BASE_URL": "https://apps.{lms-domain}"
    },
    "MFE_CONFIG_ACCOUNT": {
        "BASE_URL": "https://account.{lms-domain}"
    },
    "MFE_CONFIG_COURSE-AUTHORING": {
        "BASE_URL": "https://course-authoring.{lms-domain}"
    },
    "MFE_CONFIG_GRADEBOOK": {
        "BASE_URL": "https://gradebook.{lms-domain}"
    },
    "MFE_CONFIG_LEARNING": {
        "BASE_URL": "https://learning.{lms-domain}"
    },
    "MFE_CONFIG_PROFILE": {
        "BASE_URL": "https://profile.{lms-domain}"
    }
}