deps: update dependency com.google.cloud:gapic-libraries-bom to v1.21…

….0 (#1942)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [com.google.cloud:gapic-libraries-bom](https://togithub.com/googleapis/google-cloud-java) | `1.18.0` -> `1.21.0` | [![age](https://developer.mend.io/api/mc/badges/age/maven/com.google.cloud:gapic-libraries-bom/1.21.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://developer.mend.io/api/mc/badges/adoption/maven/com.google.cloud:gapic-libraries-bom/1.21.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://developer.mend.io/api/mc/badges/compatibility/maven/com.google.cloud:gapic-libraries-bom/1.18.0/1.21.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://developer.mend.io/api/mc/badges/confidence/maven/com.google.cloud:gapic-libraries-bom/1.18.0/1.21.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) |

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### Release Notes

<details>
<summary>googleapis/google-cloud-java (com.google.cloud:gapic-libraries-bom)</summary>

### [`v1.21.0`](https://togithub.com/googleapis/google-cloud-java/blob/HEAD/CHANGELOG.md#1210-2023-09-28)

[Compare Source](https://togithub.com/googleapis/google-cloud-java/compare/v1.18.0...v1.21.0)

##### Features

-   \[dialogflow-cx] add support for AdvancedSettings ([#&#8203;9918](https://togithub.com/googleapis/google-cloud-java/issues/9918)) ([59f9d8c](https://togithub.com/googleapis/google-cloud-java/commit/59f9d8c7ad8fc498f13873fc2b348ea23984f87c))

##### Bug Fixes

-   **deps:** update dependency com.google.cloud:google-cloud-pubsub-bom to v1.125.4 ([#&#8203;9915](https://togithub.com/googleapis/google-cloud-java/issues/9915)) ([58249cc](https://togithub.com/googleapis/google-cloud-java/commit/58249cca29b6a8a8b9075231c2e912a4553e5a2b))

##### Documentation

-   add links to rpc and rest documentation in repo-metadata.json ([#&#8203;9913](https://togithub.com/googleapis/google-cloud-java/issues/9913)) ([453c1b7](https://togithub.com/googleapis/google-cloud-java/commit/453c1b77b721731cc9175d8c57b918fcd2de7be6))

</details>

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google-cloud-bigtable-deps-bom/pom.xml

@@ -66,7 +66,7 @@
       <dependency>
         <groupId>com.google.cloud</groupId>
         <artifactId>gapic-libraries-bom</artifactId>
-        <version>1.18.0</version>
+        <version>1.21.0</version>
         <type>pom</type>
         <scope>import</scope>
       </dependency>