Warn or fail CLI commands against incompatible server versions

[Suchiman]

We haven't yet upgraded to the 2020 Release (planning on doing that in roughly a month) and i'm currently working on automating our infrastructure deployment. As part of that i need to create ApiKeys in the release pipeline.
Initially i was looking for a "Seq Powershell Management Module" and only found the C# API so i was about to write my own tool before i remembered seqcli.

I went and downloaded, without a thought, the newest version from the release page and got to work and it seemed to work, except that it didn't create any Properties. After checking and playing with fiddler i found that it sent the Properties but not in the way Seq expects them, due to #135. At that point I've noticed that the versioning scheme of seqcli appears to match the Seq versioning scheme and that probably means that there's no backcompat and the seqcli version must match the Seq server version, but there's no mention in the readme / release page nor a warning in the cli that the versions must match or you might run into incompatibilities.

A version check in the seqcli could avoid some headache for future users 😉

[nblumhardt]

Thanks for the suggestion! The Seq API provides the server version via the /api root endpoint; it should be quite straightforward for us to identify version mismatches and fail if the seqcli version is ahead of the servers' minor version.

The other way around is generally given more attention - i.e. old API clients should more often work correctly against newer server versions - but it might pay for us to investigate conservatively failing in that case, too.