What

This Merge Request fixes the encoding for version.

Why

Calling octez-client rpc get /version results in a failure in case of a Beta version.

Invalid_argument("Json_encoding.construct: consequence of bad union")

Add missing Beta and Beta_dev cases in additional_info_encoding.

Document the interface of any function added or modified (see the coding guidelines)
Document any change to the user interface, including configuration parameters (see node configuration)
Provide automatic testing (see the testing guide).
For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
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