fix: add persistent flags to root finch command

[coderbirju]

Issue #, if available: #516 Adds the global flags as persistent string flag to the root finch command. This enables the cli to display the flags when running the --help command on finch.

Description of changes:

Testing done: Verified that the command works and display the global flags.

sudo ./_output/bin/finch help build  
Build an image from Dockerfile

Usage:
  finch build [flags]

Flags:
  -h, --help   help for build

Global Flags:
      --cgroup-manager string   Cgroup manager to use ("cgroupfs"|"systemd")
      --debug                   running under debug mode
      --namespace string        containerd namespace, e.g "finch"
      --snapshotter string      containerd snapshotter

• [x] I've reviewed the guidance in CONTRIBUTING.md

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