Check for connectivity on startup

[surister]

Would it make sense to issue an SELECT 1 on startup and check if connectivity to CrateDB is possible with the given configuration? I'd say it would be helpful for users to get a clear 'Cannot connect to CrateDB', rather than some timeout error

wdyt @amotl ?

[amotl]

If that would help, sure. I don't see any immediate downsides of this, and it would improve usability. When there are no objections by others, could you add that improvement?

/cc @WalBeh, @proddata, @hlcianfagna, @hammerhead, @matriv, @widmogrod

[matriv]

Yep, I think it's good idea!