Add a config file for managed crate repos.

Currently supports one parameter: a crate import denylist.

For both crate and repo config crates, put the config file name inside the crate.

Add unit tests.

Test: cargo test, ./crate_tool import instant 1.2.3
Change-Id: Ieb8f165d98af054f434dfc487f0e2ae99b8d4aae
12 files changed