Apply config changes for CSP file uploads.

This applies configuration changes for the Flask app and adds changes to
the Dockerfile so that the build can make a CSP-specific JS bundle. It
adds `write_dotenv` script that creates the appropriate `.env` file for
the `parcel` bundler depending on how the `CSP` environment variable is
set.

- Configure K8s environment variables for Flask CSP usage
- Supply default CSP config setting to Flask app
- Declare the CSP arg in the Dockerfile
- Supply extra Docker build args to CD
- Fix top-level reference to boto3 in file_upload module
- Add back missing sample NGINX config for docker-compose build

config/base.ini

@@ -6,6 +6,7 @@ COOKIE_SECRET = some-secret-please-replace
 DISABLE_CRL_CHECK = false
 CRL_FAIL_OPEN = false
 CRL_STORAGE_CONTAINER = crls
+CSP=mock
 DEBUG = true
 ENVIRONMENT = dev
 LOG_JSON = false