Light House: Save Trace File after audit

[varghesevarampi]

What would you like to see in the library?
Lighthouse saves the trace file when the saveAudits flag has been set to true. Ideally, we should be able to pass in saveAssets: true and this should generate back a trace file.

e.g. something like below:
`const lighthouseConfig = {
formFactor: 'desktop',
saveAssets: true,
screenEmulation: {
disabled: true,
},
}

cy.lighthouse(thresholds, lighthouseConfig);`

Why?
This is very useful in diagnosing why certain lighthouse reports have a skewed values of FCP,LCP etc. by looking at the trace.

Any other information that may help understanding the need
When run manually, lighthouse generates and option to view the original trace. The core light house produce allows saving trace by running the following command lighthouse https://airhorner.com/ --chrome-flags="--window-size=1280,700" --output-path=/Users/test/lighthouse --save-assets

[mfrachet]

From what I see, the flags are passed down to lighthouse. Isnt your config working? Can you provide a repro?