feat: [Spanner] Add custom instance config operations (#5495)

* feat: Add custom instance config operations

PiperOrigin-RevId: 473928081

Source-Link: googleapis/googleapis@5440048

Source-Link: googleapis/googleapis-gen@840feec
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* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

* fix!: Revert add custom instance config operations (change broke client libraries; reverting before any are released)

PiperOrigin-RevId: 473985182

Source-Link: googleapis/googleapis@e544df5

Source-Link: googleapis/googleapis-gen@a17c20e
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* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

* feat: Add custom instance config operations

PiperOrigin-RevId: 474535825

Source-Link: googleapis/googleapis@69c840e

Source-Link: googleapis/googleapis-gen@33e360e
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* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

* manual test fix

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>
Co-authored-by: rahul2393 <[email protected]>