add comment on certifier when last-scan is set or not set

[pxp928]

Description of the PR

add comment on certifier when last-scan is set or not set

{"level":"info","ts":1728063401.121687,"caller":"certify/certify.go:109","msg":"Starting certifier run: 2024-10-04 17:36:41.121594 +0000 UTC","guac-version":"v0.0.1-custom"}
{"level":"info","ts":1728063401.1218429,"caller":"root_package/root_package.go:74","msg":"last-scan set to: 4, last scan time set to: 2024-10-04 13:36:41.121823 +0000 UTC","guac-version":"v0.0.1-custom"}
{"level":"info","ts":1728063401.241639,"caller":"certify/certify.go:114","msg":"Certifier run completed: 2024-10-04 17:36:41.241626 +0000 UTC","guac-version":"v0.0.1-custom"}

PR Checklist

• All commits have a Developer Certificate of Origin (DCO) -- they are generated using -s flag to git commit.
• All new changes are covered by tests
• If GraphQL schema is changed, make generate has been run
• If GraphQL schema is changed, GraphQL client updates/additions have been made
• If OpenAPI spec is changed, make generate has been run
• If ent schema is changed, make generate has been run
• If collectsub protobuf has been changed, make proto has been run
• All CI checks are passing (tests and formatting)
• All dependent PRs have already been merged

[funnelfiasco]

LGTM! This is a good addition for sysadmins :-)