[Dashboards] [Embeddables] Allow embeddables to register a panel config schema

[nickpeihl]

This is a WIP example for allowing embeddables to register a panel config schema that allows the Dashboard to validate panel content via the public HTTP or internal RPC CRUD endpoints.

Initially, this adds validation for Lens data table charts. An example of a chart that gets validated against the schema is below. Other Lens charts will be validated against a generic schema. Embeddables that do not register a schema are not validated.

curl --request POST \
  --url http://localhost:5601/api/dashboards/dashboard \
  --header 'accept: application/json' \
  --header 'authorization: Basic ZWxhc3RpYzpjaGFuZ2VtZQ==' \
  --header 'elastic-api-version: 2023-10-31' \
  --header 'kbn-xsrf: true' \
  --data '{"attributes": {"title": "a table lens panel","panels": [{"type": "lens","gridData": {"x": 0,"y": 0,"w": 24,"h": 15},"panelIndex": "666ba2ac-babb-4226-ad8b-9e30fec7dd74","panelConfig": {"attributes": {"visualizationType": "lnsDatatable","title": "my data table","state": {"datasourceStates": {"formBased": {"layers": {"53c6e98c-6267-4d97-876b-29f5df00e39b": {"columns": {"963714a8-b8a2-4e7d-889e-3851c74a0212": {"dataType": "string","isBucketed": true,"operationType": "terms","sourceField": "machine.os.keyword","params": {"size": 5,"orderBy": {"type": "alphabetical"}}},"627d787d-f907-46d2-861f-7752cd1001b9": {"dataType": "number","isBucketed": false,"label": "Count of records","operationType": "count","sourceField": "___records___"}},"columnOrder": ["963714a8-b8a2-4e7d-889e-3851c74a0212","627d787d-f907-46d2-861f-7752cd1001b9"]}}}},"visualization": {"layerId": "53c6e98c-6267-4d97-876b-29f5df00e39b","layerType": "data","columns": [{"columnId": "627d787d-f907-46d2-861f-7752cd1001b9"},{"columnId": "963714a8-b8a2-4e7d-889e-3851c74a0212"}]},"query": {"query": "","language": "kuery"},"filters": []},"references": [{"type": "index-pattern","id": "90943e30-9a47-11e8-b64d-95841ca0b247","name": "indexpattern-datasource-layer-53c6e98c-6267-4d97-876b-29f5df00e39b"}]}}}]},"references": [{"type": "index-pattern","id": "90943e30-9a47-11e8-b64d-95841ca0b247","name": "666ba2ac-babb-4226-ad8b-9e30fec7dd74:indexpattern-datasource-layer-53c6e98c-6267-4d97-876b-29f5df00e39b"}]}'

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