Parsing nested arrays containing multiple datasets in json_v2

Hello everybody.

I'm trying to parse mains grid frequency data from gridradar.net and got stuck. Not sure if it's me or a bug.
Every request returns mains frequency data since the last request, so the number of elements is not fixed.

If the data would look like this, everything would be easy:
```
[
{
"datapoints": [
{
"f":50.003,
"t":"2022-07-05 12:55:56"
},
{
"f":50.014,
"t":"2022-07-05 12:55:57"
},
{
"f":49.998,
"t":"2022-07-05 12:55:58"
},
{
"f":49.893,
"t":"2022-07-05 12:55:59"
}
],
"target": "median_frequency"
}
]
```

A corresponding telegraf.conf like this works well here:
```
[[inputs.file]]
files = ["./test3.json"]
data_format = "json_v2"
[[inputs.file.json_v2]]
measurement_name = "median_freq"
[[inputs.file.json_v2.object]]
path = "0.datapoints"
disable_prepend_keys = true
timestamp_format = "2006-01-02 15:04:05"
timestamp_key = "t"
```

Telegraf test output:
```
> median_freq, f=50.003 1657025756000000000
> median_freq, f=50.014 1657025757000000000
> median_freq, f=49.998 1657025758000000000
> median_freq, f=49.893 1657025759000000000
```

Now, the problem is that in reality the incoming data looks like this:
```
[
{
"datapoints": [
[
50.003,
"2022-07-05 12:55:56"
],
[
50.014,
"2022-07-05 12:55:57"
],
[
49.998,
"2022-07-05 12:55:58"
],
[
49.893,
"2022-07-05 12:55:59"
]
],
"target": "median_frequency"
}
]
```

Doing some gjson magic in GJSON Playground brought me to this conf:
```
[[inputs.file]]
files = ["./test2.json"]
data_format = "json_v2"
[[inputs.file.json_v2]]
measurement_name = "median_freq"
[[inputs.file.json_v2.object]]
path = "{datapoints:{f:0.datapoints.#.0,t:0.datapoints.#.1}.@group}"
disable_prepend_keys = true
timestamp_format = "2006-01-02 15:04:05"
timestamp_key = "datapoints.t"
```

Well, the test output is just empty.

Is this a bug, am I hitting some limitation of json_v2 or am I doing something wrong? On the Playground this looks like it should work.

Best,
Sebbi

No source files or tests are identified in the report. Reproduce the two json_v2 configurations with the nested array payload and trace how the object path is evaluated; done means determining whether this shape is supported, then fixing the behavior or documenting the limitation.

Written by the indexing model from the issue text.