Fix usage of --dangerous-allow-use-of-shared-namespace in hint

[mamachanko]

What this PR does / why we need it:

The example usage of --dangerous-allow-use-of-shared-namespace in the hint is wrong:

❯ kctrl package install --namespace default --package stuff --version 1.19.3 --package-install stuff
kctrl: Error: Creating sensitive resources in a shared namespace (default)(hint: Specify a namespace using the '-n' flag or use kubeconfig to change default namespace 'kubectl config set-context --current --namespace=private-namespace'.Or use '--dangerous-allow-use-of-shared-namespace=default' to allow use of shared namespace)

The issue in detail

use '--dangerous-allow-use-of-shared-namespace=default' to allow use of shared namespace
                                              ↑ this is wrong                         

Instead, simply show to toggle the dangerous flag:

❯ kctrl package install --namespace default --package gateway.ossistio.tanzu.vmware.com --version 1.19.3 --package-install gateway-ossistio
kctrl: Error: Creating sensitive resources in a shared namespace (default)(hint: Specify a namespace using the '-n' flag or use kubeconfig to change default namespace 'kubectl config set-context --current --namespace=private-namespace'.Or use '--dangerous-allow-use-of-shared-namespace' to allow use of shared namespace)

The new hint in detail

use '--dangerous-allow-use-of-shared-namespace' to allow use of shared namespace
                                             ↑ this is better

Which issue(s) this PR fixes:

Fixes #

Does this PR introduce a user-facing change?

Additional Notes for your reviewer:

Review Checklist:

• Follows the developer guidelines
• Relevant tests are added or updated
• Relevant docs in this repo added or updated
• Relevant carvel.dev docs added or updated in a separate PR and there's
  a link to that PR
• Code is at least as readable and maintainable as it was before this
  change

Additional documentation e.g., Proposal, usage docs, etc.:

[100mik]

Nice catch! Looks good to me 🚀