feature/tailnetlock/tslockjsonv1: turn print functions into JSON converters

This patch pulls the printing and JSON-encoding out of
feature/tailnetlock/tslockjsonv1 into their callers, so that this
package only handles type conversions.

In cmd/tailscale/cli/tailnet-lock.go, it extracts the
printTailnetLockStatus function from runTailnetLockStatus to mirror
printTailnetLockLog and runTailnetLockLog.

Updates #17613

Signed-off-by: Simon Law <sfllaw@tailscale.com>