Cannot load feature flag config values from a config file

A config file like this:

```JSON
{
"feature-flags": {
"newAutoRefresh": "false"
}
}
```

or this:
```TOML
[feature-flags]
newAutoRefresh = "false"
```

or even this:

```YAML
feature-flags:
newAutoRefresh: "false"

```

Results in this error:
```
021-12-21T21:02:29.723346Z info Welcome to InfluxDB {"log_id": "0YZhgaLl000", "version": "dev", "commit": "ca0bec4768", "build_date": "2021-12-21T21:02:29Z"}
2021-12-21T21:02:29.723868Z debug loaded config file {"log_id": "0YZhgaLl000", "path": "/Users/wbaker/influxdb/cmd/influxd/config.json"}
2021-12-21T21:02:29.724136Z error Failed to configure feature flag overrides {"log_id": "0YZhgaLl000", "error": "configured overrides for non-existent flags: newautorefresh", "overrides": {"newautorefresh":"false"}}
Error: configured overrides for non-existent flags: newautorefresh
See 'influxd -h' for help
```

Start by reproducing the reported error with the JSON, TOML, and YAML examples, then trace config loading through feature-flag override validation. Done means valid feature-flag values from these config formats load without being reported as overrides for nonexistent flags.

Written by the indexing model from the issue text.