refactor: Terraform to seed causes and donations test data to Firestore

[rogerthatdev]

Related to #644

This adds the following to the emblem-app terraform module:

• a Firestore document resource for each object in a causes.json file
• a Firestore document resource for each object in a donations.json file

The above uses Terraform templates and json files made up from data in sample_data.json

Note: merging this PR will not change any Terraform functionality. The seed_test_data variable used is set to false by default so that none of the resources associated with test data is added. The resources in this module will remain dormant until seed_test_data is set to true

This will only partially address #602

Forthcoming PR will integrate these features with setup.sh

[engelke]

LGTM