OAS-20 push code

[rpigu-i]

Handles:

1. Kicking off the CodeBuild CI pipeline
2. Accepting parameters from a JSON files and/or the commandline
3. Checking code out of GitHub
4. Migrating code into S3 Bucket.

TODO:

1. Cache invalidation for CloudFront
2. Review mechanism that injects commands into CloudBuild and see if this approach works for MVP
3. Review DNS versus EMail for Cert manager
4. Add logic to ensure specified flags override commandline params and parameters in a config file.
5. Init command wrapper for all the separate steps.

N.B The order of precedence is:

Specified flags > key/values in site_config parameter > key/values in file defined by site_config_file parameter

e.g.

--dom example.com > --site_config {"dom": "example.com" } > --site_config_file mydomainconfig.json