Logrus hooks for terminal vs log-file output

[Inspector-Butters]

Review after #16059

What type of PR is this?
Feature

What does this PR do?
This PR introduces logrus writer hooks into the logging of prysm.
when log-format is text:

• set the default logrus output to be io.Discard
• create a writer hook for terminal, with formatting and coloring enabled.
• create a separate writer hook for log-file (if enabled), without coloring.

This immediately allows for having formatted/colored terminal logs, while keeping the log-file clean.