Changes the RPC header format from `codervpn <version> <role>` to
`codervpn <role> <version1,version2,...>`.
The versions list is a list of the maximum supported minor version for
each major version, sorted by major versions.
E.g. `1.0,2.3,3.1` means `1.0, 2.0, 2.1, 2.2, 2.3, 3.0, 3.1` are
supported.
When we eventually support multiple versions, the peer's version list
will be compared against the current supported versions list to
determine the maximum major and minor version supported by both peers.
Closes#15601
