feat: Add support for Node 18, 20 drop support for Node 12

[dplewis]

https://github.com/actions/runner-images/blob/main/images/linux/Ubuntu2204-Readme.md#nodejs

There was a fix in the http2 module to correctly handle errors. Before we had to parse the error in the end event now its handled on error emitter on client requests.

Closes: #132

This PR is referencing #131, which has now been closed.

[parse-github-assistant[bot]]

Thanks for opening this pull request!

[codecov[bot]]

Codecov Report

All modified lines are covered by tests :white_check_mark:

Comparison is base (a25c835) 93.53% compared to head (9370b2f) 93.53%. Report is 1 commits behind head on master.

:exclamation: Current head 9370b2f differs from pull request most recent head e831e6f. Consider uploading reports for the commit e831e6f to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #137 +/- ## ======================================= Coverage 93.53% 93.53% ======================================= Files 23 23 Lines 588 588 ======================================= Hits 550 550 Misses 38 38 ```

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[parseplatformorg]

🎉 This change has been released in version 6.0.0

[wojtekmaj]

https://github.com/parse-community/node-apn/blob/master/package.json#L68 package.json engines was still left out :)

[mtrezza]

@wojtekmaj Thanks, you are right, do you want to open a quick PR?

[wojtekmaj]

@mtrezza Done. Also, repository settings must be updated to require new tests and unrequire removed ones, but that needs to be done by the maintainer :)

[mtrezza]

Thanks, done in https://github.com/parse-community/node-apn/pull/138