feat: update GAPIC samples to be featured in create message guide

[PierrickVoulet]

Description

Porting edits based on golden https://github.com/googleworkspace/python-samples/pull/1690.

Is it been tested?

• [X] Development testing done

Checklist

• [X] My code follows the style guidelines of this project
• [X] I have performed a self-review of my own code
• [X] I have performed a peer-reviewed with team member(s)
• [X] I have commented my code, particularly in hard-to-understand areas
• [X] I have made corresponding changes to the documentation
• [X] My changes generate no new warnings
• [X] Any dependent changes have been merged and published in downstream modules

[snippet-bot[bot]]

Here is the summary of changes.

You are about to delete 1 region tag.

- [chat/client-libraries/cloud/src/main/java/com/google/workspace/api/chat/samples/CreateMessageAppCredWithCards.java:20](https://github.com/googleworkspace/java-samples/blob/b59745f664d959d3d39fdf1b935d812e67c01c13/chat/client-libraries/cloud/src/main/java/com/google/workspace/api/chat/samples/CreateMessageAppCredWithCards.java#L20), tag `chat_CreateMessageAppCredWithCards`

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