Added onChild callback with tests and documentation

[Diabl0269]

As discussed in this issue #1534, i've added an onChild callback that uses the child instance as its argument.
I also included tests and documentation.

Please let me know if anything should be change :)

[mcollina]

Good work! Can you please add a test for the type in https://github.com/pinojs/pino/blob/master/test/types/pino.test-d.ts?

[Diabl0269]

Thanks you!
First time I use tsd so I hope I did it right.
Over then that I updated the onChild type to recognize it as an initialization option as well as a property on the logger. (The JS actually works for both but the type was missing).

[mcollina]

lgtm

[Diabl0269]

Thanks again!
I don't have permission to merge the PR, will you give me the permission/merge it?

[mcollina]

Let's wait a few more reviews, then I'll merge and ship this.

[jsumners]

Does the callback block child creation? Do we handle any errors that occur within the callback?

[Diabl0269]

The callback doesn't block the child creation, unless the it throws an error.
Should we wrap the callback in a try-catch block?

[jsumners]

I think the way the callback is handled should be made clear in the documentation. Adding a try/catch during child creation will have a performance penalty. So we would want to alter the documentation to make it clear that any error in the callback will be uncaught.

[Diabl0269]

Got it. I've updated the documentation to mention the callback doesn't handle errors.

[mcollina]

@jsumners PTAL

[jsumners]

Looks good to me.

[github-actions]

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