better errors in `edgedb instance create`

cc @raddevon @fantix @tailhook @elprans

A few issues:

1. Currently, the message says:

I suggest the following wording:

> Waiting for the `1st1/test` instance to be created. This operation may take a few minutes.

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2. When ^C is hit we currently show:

We should do better than that; showing a warning log entry is no good. But even the log entry should read:

> Exiting due to a keyboard interrupt (Ctrl+C)

But we should print a message, clarifying that we've only stopped waiting to hear back from the cloud:

> Error: aborting the wait due to Ctrl+C. The `1st1/test` instance is still pending to be created.

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3. When removing an instance we show the following error:

We should interpret the HTTP status code and report back:

> Error: no instance named `1st1/test` found.

4. Creating an instance with an already used name:

Again, need to do a better job with error reporting. The tool should say

> Error: an instance named `1st1/test` already exists.

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5. The above screenshot also shows what happens when you need to confirm instance deletion and type anything but "yes". The tool just craps out with `edgedb error: Canceled`. We should instead say:

> Cancelling deletion of `1st1/test`. The operation was not confirmed with a "yes".