[Playground] Setup Datastore in Playground project using Terraform - change main.tf file

[MakarkinSAkvelon]

Since ShareAnyCode required Datastore, there are couple of changes in this Pull Request, related terraform changes:

1. Datastore was added in App Engine and database type was defined
2. Setup Datastore

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[olehborysevych]

LGTM (internal review)

[MakarkinSAkvelon]

R: @damondouglas

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