Teach gecko profile processing to use the marker schema to properly offset timestamps

Right now we have lots of custom handling. This could be done purely with marker schema.

e.g. for Network markers:

```
if (newData.type === 'Network') {
if (typeof newData.domainLookupStart === 'number') {
newData.domainLookupStart += delta;
}
if (typeof newData.domainLookupEnd === 'number') {
newData.domainLookupEnd += delta;
}
if (typeof newData.connectStart === 'number') {
newData.connectStart += delta;
}
```

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-311)