feat(bigquery/connection): add cloud spanner connection properties - …

…serverless analytics (googleapis#7487)

feat: add cloud spanner connection properties - database role

PiperOrigin-RevId: 511807110

Source-Link: googleapis/googleapis@a563815

Source-Link: https://github.com/googleapis/googleapis-gen/commit/a28f65acace12504dfe448b2bdc5513ee8986265
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