Refs #26822
AWS says to treat 503 errors, at least in the case of ec2 metadata query, as backoff-retry (generally, we do _not_ retry on provider level, but delegate this to higher levels). This patch adds special treatment for 503:s (service unavailable) for both ec2 meta and actual endpoint, doing exponential backoff.
Note: we do _not_ retry forever.
Not tested as such, since I don't get any errors when testing (doh!). Should try to set up a mock ec2 meta with injected errors maybe.
Closesscylladb/scylladb#26934
* github.com:scylladb/scylladb:
encryption::kms_host: Add exponential backoff-retry for 503 errors
encryption::kms_host: Include http error code in kms_error
6f6ee5581e