Static mappings are generated for dynamic fields definitions

[jsoriano]

Fields definitions for dynamic mappings generate the dynamic mapping, but also an static mapping with a member named *. This seems unexpected.

For example the following field definition:

    - name: core.*.pct
      type: object
      object_type: scaled_float
      format: percent
      description: >
        Percentage of CPU time in this core.

Produces these mappings (as seen with metricbeat export template):

  "template": {
    "mappings": {
      ...
      "dynamic_templates": [
         ...
         {
          "docker.cpu.core.*.pct": {
            "mapping": {
              "scaling_factor": 1000,
              "type": "scaled_float"
            },
            "match_mapping_type": "*",
            "path_match": "docker.cpu.core.*.pct"
          }
        },
        ...
      ],
      "properties": {
        "docker": {
          "properties": {
            ...
            "cpu": {
              "properties": {
                "core": {
                  "properties": {
                    "*": {
                      "properties": {
                        "pct": {
                          "type": "object"
                        },
                        ...
                      }
                    }
                  }
                },
             }
      ...

The dynamic mapping seems correct, but the other one looks like a static definition for an object field called literally docker.cpu.core.*.pct, what seems unexpected.

Found while investigating https://github.com/elastic/kibana/issues/129344#issuecomment-1201575075.

[elasticmachine]

Pinging @elastic/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)

[botelastic[bot]]

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