Provide a way to check if an org/bucket exists.

Proposal:
Provide methods for checking for the existence of a particular org or bucket by name.

Current behavior:
BucketsAPI.getBuckets({ orgId, name }) will throw if the bucket with the provided name is not found, rather than returning an empty array of buckets as expected.

Desired behavior:
To get back an empty array of buckets if no bucket with the provided name exists.

Alternatives considered:
The samples imply that the user should catch the exception and then proceed, but this is considered a bad pattern. Exceptions should not be used for code flow, they should be exceptional. In my case, it is very reasonable that a bucket doesn't yet exist with the provided name but I have no way (using this library) to first check to see if a particular bucket exists before trying to create it.

Use case:
Exceptions should not be used for flow control, but currently that appears to be the only way to check for bucket existence. This means if I run my script in a debugger and enable "break on exceptions", my code will break in a non-exceptional code path.

The fact that you get a possibly undefined array of buckets implies to me (the library user) that I should except to get back an empty array (or maybe undefined array) if the provided bucket doesn't exist, but this isn't the case.

Start at the BucketsAPI.getBuckets({ orgId, name }) entry point described in the issue and trace how a missing bucket is handled. Check the surrounding API surface for an existing organization or bucket lookup method; done means a missing named bucket can be checked without an exception and returns the expected empty result.