Add awaitDebugger() helper to wait for Chrome DevTools to be up

[joffrey-bion]

In some use cases, the DevTools debugger server might take some time to start, and it is not always obvious how to synchronize with it. The current HTTP client doesn't have any retry and just fails when attempting to connect if it's too early (see #173).

It might be useful for such use cases to have a dedicated function call in the code to wait for the debugger server to be up, such as ChromeDPClient.awaitDebugger().

As mentioned in the related issue (linked above), this can be implemented by using retries. Exposing the Ktor client's retry configuration is a quick win, but ties this project further with Ktor, which might not be desirable. This is to be taken into consideration during design.