Add namespace webhook validation

[michael-valdron]

Please specify the area for this PR

registry operator

What does does this PR do / why we need it:

Adds namespace validation to webhooks for devfileregistry, devfileregistries, and clusterdevfileregistrieslist to prevent deployment to the default namespace.

Which issue(s) this PR fixes:

Fixes #?

part of devfile/api#1092

PR acceptance criteria:

• Test Coverage
  • Are your changes sufficiently tested, and are any applicable test cases added or updated to cover your changes?
• Gosec scans
  • Fix all MEDIUM and higher findings and/or annotate a finding per gosec instructions: https://github.com/securego/gosec#annotating-code to address why a finding is not a security issue

Documentation

• Does the registry operator documentation need to updated with your changes?

How to test changes / Special notes to the reviewer:

[openshift-ci]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: kim-tsao, michael-valdron

The full list of commands accepted by this bot can be found here.

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• OWNERS

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[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (main@e29b302). Click here to learn what that means.
Patch coverage: 54.83% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #41   +/-   ##
=======================================
  Coverage        ?   22.72%           
=======================================
  Files           ?       23           
  Lines           ?     1307           
  Branches        ?        0           
=======================================
  Hits            ?      297           
  Misses          ?      995           
  Partials        ?       15           

Impacted Files	Coverage Δ
...i/v1alpha1/clusterdevfileregistrieslist_webhook.go	71.87% <20.00%> (ø)
api/v1alpha1/devfileregistrieslist_webhook.go	72.72% <33.33%> (ø)
api/v1alpha1/devfileregistry_webhook.go	60.00% <60.00%> (ø)
api/v1alpha1/validate.go	93.87% <100.00%> (ø)

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