feat: use Terraform for infrastructure description.

Implemented in the following commits:
- 45b9537
- 2bd8d05
- 92b74da
- 0e8a7f1
- 57b196d
- cc0c59c
- 65d12fc

Fix #1000

[skip ci]

Author: php-coder

NEWS.txt

@@ -2,7 +2,8 @@
 - (feature)        add support for Ukrainian hryvnia
 - (feature)        add support for Belarusian ruble
 - (feature)        a request that failed to download a file, can be retried
-- (infrastructure) Migrate to Spring Boot 2
+- (infrastructure) migrate to Spring Boot 2
+- (infrastructure) apply infrastructure-as-code approach with Terraform
 
 0.4.2
 - (feature)        users can add multiple instances of a series into a collection

infra/terraform/my-stamps.tf

@@ -1,4 +1,6 @@
 # @todo #1000 CI: validate and check Terraform configuration
+# @todo #1000 Terraform: add UptimeRobot
+# @todo #1000 Terraform: add Mailgun
 
 variable "do_token" {}