Standards checklist:

• The PR title is descriptive.
• I have read CONTRIBUTING.md
• The code compiles (cargo build)
• The code passes rustfmt (cargo fmt)
• The code passes clippy (cargo clippy)
• The code passes tests (cargo test)
• Optional: I have tested the code myself

For new steps

• Optional: Topgrade skips this step where needed
• Optional: The --dry-run option works with this step
• Optional: The --yes option works with this step if it is supported by
  the underlying command

If you developed a feature or a bug fix for someone else and you do not have the
means to test it, please tag this person here.

What does this PR do

1. Put step logs in a span so that we can clearly see which step a log entry belongs to.

Before:

DEBUG Cannot find "rpm-ostree"
DEBUG Detected "/usr/bin/dnf" as "dnf"
Dry running: /usr/bin/sudo /usr/bin/dnf upgrade -y

After:

DEBUG step{step=System key=System update}: Cannot find "rpm-ostree"
DEBUG step{step=System key=System update}: Detected "/usr/bin/dnf" as "dnf"
Dry running: /usr/bin/sudo /usr/bin/dnf upgrade -y