Add agentctl to https://apt.grafana.com stable main repository

[DeadNews]

Request

Current list of packages in the repository:

$ grep ^Package /var/lib/apt/lists/*grafana*_Packages | awk '{print $2}' | sort -u

grafana
grafana-agent
grafana-agent-flow
grafana-enterprise
logcli
loki
loki-canary
metaconvert
mimir
mimir-continuous-test
mimirtool
promtail
query-tee
synthetic-monitoring-agent
tempo

Is one of the following possible?

• Add agentctl to https://apt.grafana.com stable main repository.
• Or add config-check subcommand for grafana-agent binary.

Use case

grafana-agent configuration file validation.

ref: #329 (comment), ad3c9a3