Parse json keys in log

[kiaplayer]

Improvement for #115.
Allows to parse inner json objects (only one level deep).

For example, we have this log message:

{
    "message": "some message",
    "someData1": {
        "someKey1": "someValue1",
        "someKey2": "someValue2"
    },
    "someData2": {
        "someKey3": "someValue3",
        "someKey4": "someValue4"
    }
}

We'll get this data in Clickhouse:

string_fields.names	string_fields.values
['message', 'someData1.someKey1', 'someData1.someKey2', 'someData2.someKey3', 'someData2.someKey4']	['some message', 'someValue1', 'someValue2', 'someValue3', 'someValue4']

Now we can search records in Clickhouse by inner fields:

SELECT
    arrayElement(`string_fields.values`, indexOf(`string_fields.names`, 'someData1.someKey1')) AS searchValue
FROM logs
WHERE searchValue == 'someValue1'
ORDER BY timestamp DESC;