Swift log now has an InMemoryLogHandler. Lets depend on that instead of
having our own `CollectEverythingLogHandler`.
I've added an extension on top, to make it easier to create the logger
too
Result: less code
Migrate CI to use GitHub Actions.
### Motivation:
To migrate to GitHub actions and centralised infrastructure.
### Modifications:
Changes of note:
* Adopt swift-format using rules from SwiftNIO.
* Remove scripts and docker files which are no longer needed.
* Disabled warnings-as-errors on Swift 6.0 CI pipelines for now.
### Result:
Feature parity with old CI.
hamzahrmalik
Rick Newton-Rogers
David Nadoba