aws/iam: Manage IAM resources for the testing environment

[tsibley]

The "dev" policy becomes a general "non-production" policy, and we'll be able to use Terraform templating to tailor the policies to specific environments. This will be necessary for Cognito access soon.

Related issue(s)

656

Testing

• [x] Local server works
• [x] Terraform plan is as expected
• [x] Checks pass

[tsibley]

A follow up to #656 to enable cleaner work on #581. Similar to the former, I'll merge and deploy this once CI passes so the Terraform changes don't linger and I can switch usage of the IAM user nextstrain.org.dev to nextstrain.org-testing.

[tsibley]

I've applied the configuration and replaced these usages of nextstrain.org.dev with nextstrain.org-testing:

• Heroku review app config vars AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY
• DEV_SERVER_AWS_ACCESS_KEY_ID and DEV_SERVER_AWS_SECRET_ACCESS_KEY secrets for this repo

I've deactivated the two access keys for nextstrain.org.dev. If no other usages arise in the next ~24h or so, I'll remove the user entirely.

To do:

• [x] Remove IAM user nextstrain.org.dev
• [x] Remove IAM policy NextstrainDotOrgServerInstanceDev