Search API to query data crossing fields and tables

This is an experimental API, the goal is to support our search function on web map:

The result should be a mixed list, the items of the list could be: tree item, planter, org, so we need search all of them on the server, and combinate the result to a list.

API spec:
GET /search?keyword=[treeid|planter name]
response:
{
total: 10,
list: [{
type: 'tree|planter',
data: { ... tree object | planter object}
}]
}

Currently, don't need to consider pagination, just simply return up to 10 results.

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