Enable streaming of logs during Tesseract application

[dionhaefner]

Summary

Ideally, users should have a way to see live updates on running Tesseracts that are invoked across various interfaces:

1. tesseract run
2. Tesseract.from_api_path(...).apply()
3. Tesseract.from_image(...).apply()

That is, we want everything that is written to per-run logfiles to also be streamed to the terminal for (1), and similar functionality for (2) and (3) (which may be streamed to the terminal, a Python logger, or allow for programmatic access like a log generator).

Why is this needed?

$ tesseract run my-expensive-tesseract apply '...'
# hangs for 10 minutes, then prints:
Now doing x
x took 632s
Now doing y
y took 2s
Now doing z
z took ...

Usage example

tbd

[dionhaefner]

Example implementation for case (3) above in in #314.