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

• I've reviewed the guidance in CONTRIBUTING.md

License Acceptance

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.