feat(outputs.mongodb): Allow specifying metadata fields

[srebhan]

Summary

This PR allows to specify tags to be used as metadata fields. By default, the tags element is used as metadata-field to preserve backward-compatibility with existing setup. However, if a list of metadata fields is given, a new metadata element is created containing the key-value pairs with the matching tags.

Note

The new metadata_keys option accepts wildcards. All tags matching the given list will be added as metadata. If a metadata field does not match a tag it is simply ignored.

Checklist

• No AI generated code was used in this PR
• AI generated code used in this PR follows the InfluxData Policy on AI-Generated Code Contributions

Related issues

resolves #18419

[telegraf-tiger]

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