Run influxd as a child process.

Example

```rust use influxivecore::Metric; use influxivechild_svc::*;

let tmp = tempfile::tempdir().unwrap();

let influxive = InfluxiveChildSvc::new( InfluxiveChildSvcConfig { databasepath: Some(tmp.path().toowned()), ..Default::default() }, ).await.unwrap();

influxive.writemetric( Metric::new( std::time::SystemTime::now(), "my.metric", ) .withfield("value", 3.14) .with_tag("tag", "test-tag") ); ```