allow overriding the cloud operation timeout with a CLI arg or environment variable

CLI version: EdgeDB CLI 3.5.0-dev (`7292db83cf64b9eeb7ef10a83ef5262141fc466c`, master branch as of 2023-08-18)

**current behavior**

the maximum wait time for a cloud operation (instance create/upgrade/destroy) is hardcoded at 5 minutes:

https://github.com/edgedb/edgedb-cli/blob/master/src/cloud/ops.rs#L15

this is a reasonable default for users, but in testing I'm doing against the cloud I'd like to wait longer, to see how long the operation takes if there were no timeout (or a much longer timeout)

**desired behavior**

I'd like to be able to override the timeout using a CLI option or environment variable (either one would be fine, whichever is easier to implement)

**workaround**

I'm currently overriding this by changing the hardcoded default to one hour and building the CLI locally. this works, but it's a hack specific to my machine and won't work as we try to move these tests off my dev box and into a testing microservice (see https://github.com/edgedb/nebula/discussions/497)