refactor: Terraform to seed approver and donors test data to Firestore

[rogerthatdev]

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

• an approver_email variable used to indicate an initial 'approver' to add to Firebase
• a boolean seed_test_data variable, set to false by default, that toggles Firestore document resources
• a Firestore document resource using approver_email in an 'approvers' collection
• a Firestore document resource for each object in a donors.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 PRs will add test data for campaigns, causes, and donations.

[engelke]

"Seeded approver" would be better for the name

[engelke]

LGTM