rgw/cloud-restore: strip quotes from ETag on cloud tier fetch

rgw/cloud-restore: strip quotes from ETag on cloud tier fetch

When objects are restored from a cloud endpoint, the ETag value read
from the HTTP response includes surrounding double-quotes per RFC 7232.
RGW stores ETags unquoted internally, and dump_etag() adds its own
quotes when serving responses. The mismatch results in double-quoted
ETags like ""abc123-6"" on restored objects.

Strip the quotes from both the etag output parameter and the
RGW_ATTR_ETAG attribute after fetching from the cloud endpoint,
matching the unquoted format RGW uses everywhere else.

Signed-off-by: Matthew N. Heler <matthew.heler@hotmail.com>