Fixes#27242
Similar to AWS, google services may at times simply return a 503,
more or less meaning "busy, please retry". We rely for most cases
higher up layers to handle said retry, but we cannot fully do so,
because both we reach this code sometimes through paths that do
no such thing, and also because it would be slightly inefficient,
since we'd like to for example control the back-off for auth etc.
This simply changes the existing retry loop in gcp_host to
be a little more forgiving, special case 503 errors and extend
the retry to the auth part, as well as re-use the
exponential_backoff_retry primitive.
v2:
* Avoid backoff if refreshing credentials. Should not add latency due to this.
* Only allow re-auth once per (non-service-failure-backoff) try.
* Add abort source to both request and retry
v3:
* Include timeout and other server errors in retry-backoff
v4:
* Reorder error code handling correctly
Closesscylladb/scylladb#27267
(cherry picked from commit 4169bdb7a6)
Closesscylladb/scylladb#27443
ddc22a349c