[Reporting] Browser Driver is incorrectly logging browser console messages

[tsullivan]

Kibana version: 7.3.0/8.0.0

Elasticsearch version: n/a

Server OS version: n/a

Browser version: n/a

Browser OS version: n/a

Original install method (e.g. download page, yum, from source, etc.): source

Describe the bug:
We should see many more logs for browser console messages: generated by the browser, and/or generated by the web app running in the browser.

Steps to reproduce:

1. Enable verbose logging
2. Run a PDF or PNG Reporting job
3. See a single message (debug level) for a CSP error in the browser:
   

Expected behavior:

1. Since we're in verbose logging mode and seeing debug-level messages, we should be seeing a lot more logs. Example of the browser console running the same page as the dashboard in the above report:
   
2. The headless browser is attributing _type fields to each of its own logging events. We should use those to map the level of each headless-generated log to our own logging, so error logs show up with the error tag in our logs.

[elasticmachine]

Pinging @elastic/kibana-stack-services

[tsullivan]

Also, Reporting tries to log the stdout and stderr of the browser process, but it looks like that code is wrong: https://github.com/elastic/kibana/blob/7.3/x-pack/legacy/plugins/reporting/server/browsers/chromium/driver_factory/index.ts#L182

messages$ is just an observable of the console logs in the browser app. The partition probably used to work, but only for PhantomJS.

[tsullivan]

Fixed in #44359

Also, Reporting tries to log the stdout and stderr of the browser process, but it looks like that code is wrong: https://github.com/elastic/kibana/blob/7.3/x-pack/legacy/plugins/reporting/server/browsers/chromium/driver_factory/index.ts#L182

Separate issue: #44942