[K8s otel] Add exception handling for unmapped fields

[agithomas]

• Enhancement

Proposed commit message

An unmapped field is a field referenced in a query that does not exist in the mapping of the index being queried.

Certain metric points, especially related to errors, are available when the criteria are met. Also, certain resource attributes are optionally available. Add the following exception handling to avoid dashboards showing errors.

Add SET unmapped_fields="nullify";

• Determines how unmapped fields are treated. NULLIFY : Treats unmapped fields as null values.

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

• Package upgrade testing
• Data view tests.

How to test this PR locally

• elastic-package build && elastic-package stack up -v -d --services package-registry

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