Add Unleash as a service

[Dinip]

• Adds a template for Unleash, the open-source feature flag management system, along with two service flavors:
  • With Database (PostgreSQL)
  • Without Database

Docs available at: https://docs.getunleash.io/

[nunogois]

LGTM, thank you for contributing with this @Dinip!

[andrasbacsai]

Thanks for the PR!