Support for object endpoint in CouchbaseBackupRestore

the customer needs to save backups on their internal storage with S3 compatible API.

In essence, they need to have something like this:

 
cbbackupmgr config a [s3://couchbase_s3_bucket/archive] -r repo --obj-staging-dir /tmp/asd **obj-endpoint  <endpoint address> --obj-access-key-id ** --obj-secret-access-key ** -obj-region ****
 

inside the backup resource.

the command line parameter -obj-endpoint is an optional parameter with couchbase server. and CAO only supports mandatory parameters. And hence, support for this optional parameter is not implemented within CAO. Based on customer request, we need to add -obj-endpoint parameter for backup to S3 with CAO.