feat(modelarmor): Added snippets for updating templates

[harshnasitcrest]

Added following samples for Model Armor:

• Update template
• Update template with labels
• Update Template with metadata

Note:

• Please enable the Model Armor API and grant modelarmor.admin IAM permission on the service account/project that is used in this repo.
• Please ignore the create template files in this PR. Since the relevant PR is open, I've included those files to pass the tests on this PR. Once merged, I'll resolve the conflicts and then merge this PR.

[snippet-bot]

Here is the summary of changes.

You are about to add 6 region tags.

• modelarmor/src/create_template.php:29, tag modelarmor_create_template
• modelarmor/src/create_template_with_labels.php:29, tag modelarmor_create_template_with_labels
• modelarmor/src/create_template_with_metadata.php:29, tag modelarmor_create_template_with_metadata
• modelarmor/src/update_template.php:29, tag modelarmor_update_template
• modelarmor/src/update_template_labels.php:29, tag modelarmor_update_template_with_labels
• modelarmor/src/update_template_metadata.php:29, tag modelarmor_update_template_metadata

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