[FEATURE] Write logs into a file

[etiennecoutaud]

Actual behavior
Logs are streamed on stdout/stderr by default

Expected behavior
Logs output depend on a parameter.

Triage Notes for the Maintainers

If needed I can work on this and submit a PR.

Description	Yes/No
Please check if this a new feature you are proposing
Please check if the build works in docker but not in kaniko
Please check if this error is seen when you use --cache flag
Please check if your dockerfile is a multistage dockerfile

[frafra]

Seems similar to: #695

It would be interesting to have different outputs: one for the kaniko messages, another for the output produced by the RUN commands. Is that what you are looking for?