Single canonical parseable location for the version

[confluence]

There should be a single location in the repository where the current version is stored, and this information should be parsed and used in these places instead of a separate hardcoded value:

• the documentation index
• the documentation changelog
• the frontend
• the backend

Currently the primary location for this value is the documentation changelog, but it's embedded in a markdown table and not easily parseable. I think that what we need is a separate machine-readable changelog file.

Bumping the protobuf submodule in the backend or frontend should be sufficient to update the ICD version in those repos.

This will eliminate a lot of annoyance involved in keeping the values in all these locations in sync.