Add `minimal_versions` CI job

[ilslv]

Revealed from https://github.com/clap-rs/clap/pull/3172

Actual minimal versions of log is 0.4.4, not 0.4 and 1.0.113 for serde.
To avoid similar issues, I've also added minimal_versions CI job, which downgrades all crates to minimal compatible versions and runs tests on them. Although it's nightly feature for cargo, we use it throughout multiple projects and never had any issues with it.