* Add per-collector subcommands to the collect binary
Add `collect http|postgres|mysql|mssql|redis` subcommands that run a single
collector and print its native result JSON to stdout, so a collector can run
inside a Pod via the troubleshoot image (e.g. as a runPod collector).
Each has its own flags mapping to the collector's spec fields and its own help.
The Kubernetes client (used only for TLS-from-Secret) is built to match the
production preflight/support-bundle path (QPS/Burst/UserAgent).
* Add clickhouse subcommand to the collect binary
Add `collect clickhouse`, matching the other per-collector subcommands, so the
clickhouse collector can run inside a Pod via the troubleshoot image (e.g. as a
runPod collector). Same flags as the other database collectors (--uri + --tls-*).
* Make global flags work on the collect subcommands
Register --debug and the Kubernetes flags (--kubeconfig, --context, etc.) as
persistent flags, and move the shared setup to PersistentPreRun/PersistentPostRun,
so the per-collector subcommands inherit the global flags and run the same
logger/profiling setup as `collect [url]`. Previously these were local flags with
setup in PreRun, so subcommands rejected --debug/--kubeconfig and ignored the setup.
