[Kibana logging system] Add conditional evaluation based on level for logging APIs (#187225)

## Summary

*(Yeah, the title is pretty bad I apologize, I couldn't find something
sexy. OTOH, "sexy" and "logging" are usually antonyms, like "sport car"
and "fiat panda", or "server language" and "javascript")*

### 1. Provide a more developer-friendly alternative to
`Logger.isLevelEnabled`.


**With `isLevelEnabled`**
```ts
if(logger.isLevelEnabled('info')) {
  const message = someExpensiveMessageProbablyBasedOnJsonStringifyOrSomething(); 
  logger.info(message);
}
```

**With this PR:**
```ts
logger.info(() => someExpensiveMessageProbablyBasedOnJsonStringifyOrSomething());
``` 

### 2. Adapt calls to `log.debug` (arguably) costly to use this syntax

Aka any call relying on `JSON.stringify` or function calls.

I used the new syntax for those, except when the tests were too
complicated to fix or when the code did not allow it (e.g. untyped let
variables infered from return from assignations don't play well with
closures)

packages/kbn-cli-dev-mode/src/log_adapter.ts

@@ -10,8 +10,12 @@ import { Logger } from '@kbn/logging';
 import { Log } from './log';
 
 export const convertToLogger = (cliLog: Log): Logger => {
-  const getErrorMessage = (msgOrError: string | Error): string => {
-    return typeof msgOrError === 'string' ? msgOrError : msgOrError.message;
+  const getErrorMessage = (msgOrError: string | (() => string) | Error): string => {
+    return typeof msgOrError === 'function'
+      ? msgOrError()
+      : typeof msgOrError === 'string'
+      ? msgOrError
+      : msgOrError.message;
   };
 
   const adapter: Logger = {