[DOCS] Tweak Template Syntax-related docs for OP

[ArunPiduguDD]

What does this PR do? What is the motivation?

Makes some small tweaks to the Template Syntax docs for OP, specifically the table detailing the default behavior when template fields cannot be resolved:

• For the Google Chronicle destination, the default log-type should be DATADOG instead of vector_dev
• Changed some language around the the other destinations to make it slightly more accurate

[maycmlee]

/merge

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2025-02-05 19:20:15 UTC ℹ️ MergeQueue: merge request added to the queue

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2025-02-05 19:27:11 UTC ℹ️ MergeQueue: This merge request was merged

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Modified Files

• https://docs-staging.datadoghq.com/arun.pidugu/op-tweak-template-syntax-docs/observability_pipelines/destinations/