Testnet release test-5.2.0

[abit]

New testnet release "test-5.2.0" https://github.com/bitshares/bitshares-core/releases/tag/test-5.2.0 with new API, Ubuntu 20.04 LTS support and more.

Testnet API nodes please upgrade and test. Other nodes are recommended to upgrade too, although not required.

More info on the release page (release notes, binaries, docker and etc).