Add get_url function to Repository class

Useful especially for S3 repo, where we need to generate the presigned URL to enable trigger_deployment function to access the URL with the artifact. See https://boto3.amazonaws.com/v1/documentation/api/latest/guide/s3-presigned-urls.html?highlight=presigned#presigned-urls

Above description became invalid in light of !28 (comment 6135541)