This version will start generating `lucicfg {...}` section in
project.cfg, but only when some other config file changes (so
that lucicfg version change itself doesn't require all configs
to be regenerated).

This information will be used by LUCI tooling to figure out how
to regenerate LUCI project configs en masse.

Use `lucicfg generate -force main.star` to forcefully generate
`lucicfg {...}` section in the existing configs.

R=iannucci@chromium.org

Change-Id: I001ceb0dae1df797c2f76c3f6a28b8420d18f4d7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3232093
Commit-Queue: Vadim Shtayura <vadimsh@chromium.org>
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>