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

atst/domain/csp/file_uploads.py

@@ -79,7 +79,7 @@ class AwsUploader(Uploader):
             "s3",
             aws_access_key_id=self.access_key_id,
             aws_secret_access_key=self.secret_key,
-            config=boto3.session.Config(
+            config=self.boto3.session.Config(
                 signature_version="s3v4", region_name=self.region_name
             ),
         )