refactor: make management controller able to create project namespaces again

[krancour]

Since #1431 we rely on a webhook to create Project namespaces synchronously. Although this was a valid decision made for well-documented reasons, one undesired side-effect has been difficulty bootstraping Kargo with a default Project already in place:

• If the Project is applied before the webhook registration, Project creation succeeds, but creation of the underlying namespace does not take place. If the manifests contain additional resources that belong in that namespace, their creation will fail.

• If the webhook registration is applied before the Project, Project creation will fail since the webhook server isn't running yet. Creation of the underlying namespace does not take place and, as above, if the manifests contain additional resources that belong in that namespace, their creation will fail.

Some unsatisfactory solutions we explored included:

• Ensuring the webhook server is ready before attempting to create the Project.

  This was deemed to be difficult, or at least annoying.

• "Create projects the hard way" by directly creating an appropriately labeled namespace.

  This loses out on the benefits of having a Project resource. Those aren't significant now, but will be of increasing consequence over time.

We settled on partially rolling back #1431, allowing for a Project's underlying namespace to be created synchronously by a webhook or asynchronously by the management controller. This ability enables a better option:

• "Create projects the hard way" by directly creating an appropriately labeled namespace, but avoid losing out on the additional benefits of having a proper Project resource by also defining that. It must precede registration of the webhook, but that's easy enough to ensure. When Kargo comes up, the Project resource will be reconciled and will "adopt" the corresponding namespace at that time (a process we're already using in the webhook since Allow Kargo to adopt existing namespaces #1443).

cc @gdsoumya

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[gdsoumya]

LGTM