feat(js-logger): enhance async logger initialization and kept log format when otel is enabled

[CptSchnitz]

No description provided.

[ronenkapelian]

1. no test for new feature:

it('should still write to the local destination when opentelemetry is enabled', async function () {
  const logger = await jsLogger({ opentelemetryOptions: { enabled: true } }, 'avi-otel.log');
  logger.info('avi otel');
  await waitForFileCreation('avi-otel.log');
  const logLine = JSON.parse(readFileSync('avi-otel.log', { encoding: 'utf-8' })) as Record<string, unknown>;
  expect(logLine).toHaveProperty('msg', 'avi otel');
});

[ronenkapelian]

collides with pino's reserved level key
it seems it will print twice "level" key
here is generated script that demonstrate it

/**
 * Demonstrates finding #2 from pr-261-js-logger-async-init-otel.md:
 * the "logger initialized" debug line in src/index.ts sets a `level`
 * property on the merging object, which collides with pino's own
 * reserved `level` output key.
 *
 * Run from packages/js-logger:
 *   node scripts/demo-level-key-collision.js
 */
const pino = require('pino');

console.log('--- raw pino: what happens when you merge an object with its own "level" key ---\n');

const logger = pino({ level: 'debug' });

// This mirrors exactly what src/index.ts does:
//   finalLogger.debug({ msg: 'logger initialized', level: pinoOptions.level ?? 'info', ... })
logger.debug({ msg: 'logger initialized', level: 'info', otelEnabled: true });

console.log('\n--- look at the raw line above: count the "level" keys ---');
console.log('there are two: pino\'s real numeric level (20 = debug), and the fake string "info"\n');

console.log('--- now show what a JSON consumer actually sees after parsing ---\n');

// Capture what pino would actually write, then parse it like a log shipper would.
const chunks = [];
const captured = pino({ level: 'debug' }, { write: (chunk) => chunks.push(chunk) });
captured.debug({ msg: 'logger initialized', level: 'info', otelEnabled: true });

const rawLine = chunks.join('');
const parsed = JSON.parse(rawLine);

console.log('raw line written by pino:');
console.log(rawLine);
console.log('\nafter JSON.parse (what Loki/ELK/Datadog/etc. would ingest):');
console.log(parsed);
console.log(
  `\n=> parsed.level is ${JSON.stringify(parsed.level)} (a string), the real numeric severity (20) is gone.`,
);

[CL-SHLOMIKONCHA]

please mind @ronenkapelian comment