pubsys: improve logging for publish-ami

[webern]

What I'd like:

During pubsys publish-ami, which is called by cargo make ami-public, certain error paths can be confusing. It can appear that an error occurred for one region only, and that the other regions were successfully made public when, in fact, no regions were made public.

This contributed to #2617. We are taking other, stronger measures to ensure that private AMIs cannot be promoted to public SSM params (these include, but are not limited to, #2621 and #2680). In addition to such stronger measures, we also want to improve error messaging.

The confusing error looked like this:

Failed to publish AMI: AMI 'ami-xyz123' in some-region-1 did not become available: Failed to reach desired state within 90 attempts for ami-xyz123 in some-region-1

It came from here:

https://github.com/bottlerocket-os/bottlerocket/blob/develop/tools/pubsys/src/aws/publish_ami/mod.rs#L173..L178

It could lead someone to believe that only one region (i.e. some-region-1) has failed to become public. In fact what it means is that one of the AMIs was detected to be unavailable, and the operation was aborted before ANY AMIs were made public.

The goal of this issue is to make this error condition more clear.
At the same time, we may want to reduce the verbosity of the "happy" path to draw more attention to error conditions.