Add major version to the protobuf package

[tiyash-basu-frequenz]

What's needed?

According to https://cloud.google.com/apis/design/versioning, All Google API interfaces must provide a major version number, which is encoded at the end of the protobuf package. For an example, look here. Also, note how this affects the directory structure there (files in version 2 go into a directory named v2).

We do not do this ATM, as is evident here. We need to do this before we make the first stable release (v1.0.0).

Proposed solution

As mentioned here, look here for an example.

Use cases

This achieves two objectives:

1. services, in theory, could start supporting multiple major versions, to support clients while they transition.
2. adopt it as a standard in the organization, regardless of whether point 1 is valid for some services or not.

Alternatives and workarounds

No response

Additional context

No response