aws_bedrock: tolerate non-object elements in invocation output.outputBodyJson lists

[efd6]

Proposed commit message

aws_bedrock: tolerate non-object elements in invocation output.outputBodyJson lists

Some models will include string elements in this list in chat streaming
responses, so promote non-object elements to an object with a single
"value" field holding the original element value. Without this change
those documents are otherwise rejected during ingest since flattened
fields may not contain non-object elements.

The test case is a copy of an existing test case, with the final element
in the list replaced with the string "[DONE]" to reflect the original
report.

Checklist

• I have reviewed tips for building integrations and this pull request is aligned with them.
• I have verified that all data streams collect metrics or logs.
• I have added an entry to my package's changelog.yml file.
• I have verified that Kibana version constraints are current according to guidelines.
• I have verified that any added dashboard complies with Kibana's Dashboard good practices

Author's Checklist

• [ ]

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